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neomax
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Is there a minimum "rest" time for an aircraft?

Thu May 03, 2018 12:31 am

Assuming a hypothetical scenario where turnaround, catering, fueling time is not a factor, is there such a thing as a required minimum "rest" time for an aircraft to spool down to idle and cool on the ground, or can it be sent back up as soon as it is ready?
 
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william
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Re: Is there a minimum "rest" time for an aircraft?

Thu May 03, 2018 12:35 am

For the engines I believe. Just a cool down period.
 
32andBelow
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Re: Is there a minimum "rest" time for an aircraft?

Thu May 03, 2018 12:44 am

[list=][/list]
william wrote:
For the engines I believe. Just a cool down period.

Breaks too.
 
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atcsundevil
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Re: Is there a minimum "rest" time for an aircraft?

Thu May 03, 2018 12:53 am

32andBelow wrote:
Breaks too.

Breaks for brakes :D
 
727200
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Re: Is there a minimum "rest" time for an aircraft?

Thu May 03, 2018 1:06 am

Planes make no money on the ground. Get them up.
 
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Re: Is there a minimum "rest" time for an aircraft?

Thu May 03, 2018 1:32 am

Someone authorized has to dispatch.
 
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Blimpie
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Re: Is there a minimum "rest" time for an aircraft?

Thu May 03, 2018 2:03 am

I've seen the Alleigent Mad Dogs @HGR sit for less than 45 minutes before turn around which I found to be quite short.
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SkyVoice
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Re: Is there a minimum "rest" time for an aircraft?

Thu May 03, 2018 3:00 am

727200 wrote:
Planes make no money on the ground. Get them up.


That's one way that Southwest has remained profitable. On their multi-stop itineraries, their ETAs and ETDs are 20 to 25 minutes. I was at Louisville once, waiting for a Southwest flight to Midway. The inbound aircraft arrived from Birmingham ten minutes late. After a whole lot of scrambling, we departed for MDW on time. WN's people at SDF got that flight turned around in only TEN MINUTES ! ! !
"Son, don't ever try to make sense out of nonsense." - my grandmother
 
Woodreau
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Re: Is there a minimum "rest" time for an aircraft?

Thu May 03, 2018 11:25 am

Usually the limiting factor is not related to the limitations of the airplane - it is the time for passengers to deplane and board - and passengers just don't move with a sense of urgency.

My first airline scheduled 10 minute turns at the outstation - 20 minutes at the hub.

The fastest we were able to turn the aircraft was 1 minute, i.e. blocked in, then blocked out for the next flight 1 minute later.

It was for turns where we didn't have anyone get off and no one boarded. In that case, we pre-briefed the turn in the air as part of the approach briefing and coordinated with ops when we checked in prior to landing.
Basically, we blocked in, shut down #1, left #2 running, the FO got out and did his post-flight/pre-flight walkaround. While he was doing his walkaround, the ground agent handed the dispatch paperwork through the cockpit window. I scanned the paperwork to make sure all was in order, signed it and handed the release and the weight and balance paperwork back out the window - just as the FO got back in the aircraft from the walkaround and closed the passenger door. Started #1 and blocked out.

Basically our On-In and Out-Off times for the turn was On at 10, In at 11, Out at 12, Off at 13.

Sometimes we would beat the freight guy who either just landed before or after our flight and all he had to do was meet the UPS/FedEx guy and throw the cargo bag into the back of his plane and depart.
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parapente
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Re: Is there a minimum "rest" time for an aircraft?

Thu May 03, 2018 12:28 pm

As everyone is saying,turnaround times are critical to profitability,they only 'earn in the air'.As Woodreau says the time limiting factor are the passengers.Both off and on.
We see the average size of LCC aircaft going up and up and up.Some are now flying A321's that will be able to take 240 pax!Southwest has moved to 8's and Ryanair is now making positive noises about getting 10's.
If the 'on ground' is a passenger problem now,then imagine what it's going to be like with 230-240 pax per flight!

Solution?
The Boeing 797 with twin aisles.
Or
More front and rear door deplaning and boarding.Ryanair are keen on this,don't know about others.
 
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akiss20
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Re: Is there a minimum "rest" time for an aircraft?

Thu May 03, 2018 3:57 pm

Woodreau wrote:
Usually the limiting factor is not related to the limitations of the airplane - it is the time for passengers to deplane and board - and passengers just don't move with a sense of urgency.

My first airline scheduled 10 minute turns at the outstation - 20 minutes at the hub.

The fastest we were able to turn the aircraft was 1 minute, i.e. blocked in, then blocked out for the next flight 1 minute later.

It was for turns where we didn't have anyone get off and no one boarded. In that case, we pre-briefed the turn in the air as part of the approach briefing and coordinated with ops when we checked in prior to landing.
Basically, we blocked in, shut down #1, left #2 running, the FO got out and did his post-flight/pre-flight walkaround. While he was doing his walkaround, the ground agent handed the dispatch paperwork through the cockpit window. I scanned the paperwork to make sure all was in order, signed it and handed the release and the weight and balance paperwork back out the window - just as the FO got back in the aircraft from the walkaround and closed the passenger door. Started #1 and blocked out.

Basically our On-In and Out-Off times for the turn was On at 10, In at 11, Out at 12, Off at 13.

Sometimes we would beat the freight guy who either just landed before or after our flight and all he had to do was meet the UPS/FedEx guy and throw the cargo bag into the back of his plane and depart.


Dumb question but what exactly happened here? You can't get fuel in one minute, and you said no passengers boarded or deplaned, same presumably for freight so what was the point of landing?

Again stupid question which has a simple answer I assume.
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nws2002
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Re: Is there a minimum "rest" time for an aircraft?

Thu May 03, 2018 6:44 pm

Blimpie wrote:
I've seen the Alleigent Mad Dogs @HGR sit for less than 45 minutes before turn around which I found to be quite short.


Standard outstation turn times at G4 are as follows:
A319 - 40 min
MD-80 - 40 min
A320 - 45 min

Honestly, this is pretty typical for most airlines in the US.
 
fdxtulmech
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Re: Is there a minimum "rest" time for an aircraft?

Fri May 04, 2018 4:08 am

When I was working for the regionals, we made up a lot of time on turns. The plane would come in 20-30 minutes late on a 45 minute turn and leave a few minutes early. Especially, when they were tankering fuel for short hops.
 
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glen
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Re: Is there a minimum "rest" time for an aircraft?

Fri May 04, 2018 7:14 am

With very optimized ground processes (e.g. cabin cleaning starting already from the rear entrance while passengers still deboard through the front door into the jetty) we managed to turn an in- and outbound full A320 in about 30 to 35 minutes. But ervery small disturbance in the process will ruin such an optimized turnaround.
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Woodreau
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Re: Is there a minimum "rest" time for an aircraft?

Fri May 04, 2018 10:18 pm

akiss20 wrote:
Dumb question but what exactly happened here? You can't get fuel in one minute, and you said no passengers boarded or deplaned, same presumably for freight so what was the point of landing?

Again stupid question which has a simple answer I assume.


It’s a scheduled 121 flight. So you still go whether there’s no passengers on board. Coming or going.

Fuel was tankered so no fueling for this turn.

The aircraft does not have a single point fuel and has to be overwing fueled so usually the fuel truck fuels the left wing first in order to allow boarding while fueling. Sometimes two fuel trucks will show up and both tanks could be fueled simultaneously.
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strfyr51
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Re: Is there a minimum "rest" time for an aircraft?

Fri May 04, 2018 10:25 pm

Woodreau wrote:
Usually the limiting factor is not related to the limitations of the airplane - it is the time for passengers to deplane and board - and passengers just don't move with a sense of urgency.

My first airline scheduled 10 minute turns at the outstation - 20 minutes at the hub.

The fastest we were able to turn the aircraft was 1 minute, i.e. blocked in, then blocked out for the next flight 1 minute later.

It was for turns where we didn't have anyone get off and no one boarded. In that case, we pre-briefed the turn in the air as part of the approach briefing and coordinated with ops when we checked in prior to landing.
Basically, we blocked in, shut down #1, left #2 running, the FO got out and did his post-flight/pre-flight walkaround. While he was doing his walkaround, the ground agent handed the dispatch paperwork through the cockpit window. I scanned the paperwork to make sure all was in order, signed it and handed the release and the weight and balance paperwork back out the window - just as the FO got back in the aircraft from the walkaround and closed the passenger door. Started #1 and blocked out.

Basically our On-In and Out-Off times for the turn was On at 10, In at 11, Out at 12, Off at 13.

Sometimes we would beat the freight guy who either just landed before or after our flight and all he had to do was meet the UPS/FedEx guy and throw the cargo bag into the back of his plane and depart.



And? That was what Airplane Model? And? What Airport?? The airplane didn't need either Fuel,Food, Nor potable water and probably didn't need a jetway.
no crew change, nor cabin refreshments. I won't call a BS but you'd be darn close to it. I worked airlines from 1980-2017 and I NEVER saw that quick of a turn. anyplace by anybody. especially in airline servce. What were you flying Beech 99's??
 
strfyr51
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Re: Is there a minimum "rest" time for an aircraft?

Fri May 04, 2018 10:32 pm

There is no minimum Rest time for an airplane, But there is Minimum maintenance and servicing time. As long as the log book is addressed and released?
and everything is operating as advertised? You can push on. I've seen B747's B767's B777's make multiple turns from international trips as long as they had no pressing Maintenance issues.
 
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Re: Is there a minimum "rest" time for an aircraft?

Fri May 04, 2018 11:55 pm

strfyr51 wrote:
And? That was what Airplane Model? And? What Airport?? The airplane didn't need either Fuel,Food, Nor potable water and probably didn't need a jetway.no crew change, nor cabin refreshments. I won't call a BS but you'd be darn close to it. I worked airlines from 1980-2017 and I NEVER saw that quick of a turn. anyplace by anybody. especially in airline servce. What were you flying Beech 99's??


When the original Wright Amendment was in place before Missouri was added about anything WN had headed north out of DAL had to stop in OKC or sometimes TUL on their way to COS, MCI, STL, MDW etc
Fuel was 11 cents a gallon so it was tankered and there was a flight DAL-OKC-XXX about every hour during the day from DAL with a 732. The gate times were 15 minutes. 30-45 people and three bags off and about the same loaded. No additional catering was needed after just a short 25 minute flight.

********
The other flights for instance OKC-PHX-TUL- OKC had about 30 minute times because they had to fuel and cater.

Okie
 
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Re: Is there a minimum "rest" time for an aircraft?

Sat May 05, 2018 2:26 am

As we said in MAC, the only rest had during “crew rest” is for the plane.

GF
 
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Starlionblue
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Re: Is there a minimum "rest" time for an aircraft?

Sat May 05, 2018 2:26 am

Brakes and engines as mentioned. Another limiting factor is fueling time, though that is more of an issue with widebodies.
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reidar76
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Re: Is there a minimum "rest" time for an aircraft?

Sat May 05, 2018 9:30 am

strfyr51 wrote:
That was what Airplane Model? And? What Airport?? The airplane didn't need either Fuel,Food, Nor potable water and probably didn't need a jetway.no crew change, nor cabin refreshments. I won't call a BS but you'd be darn close to it. I worked airlines from 1980-2017 and I NEVER saw that quick of a turn. anyplace by anybody. especially in airline servce.


When operating short haul flights in Europe, 20 minutes on the ground is common for 737 and A320 family aircraft.

Here is an real world example: Scandinavian Airlines flight SK4144, usually a 737-700 with 141 seats (2-class, SAS Plus and SAS Go). This is a flight from SVG to TRD, which stops at BGO and AES. Connects to jetbridges at all airports. Breakfast is served onboard this morning flight. Passengers going to the next city remain onboard during ground stops. Most passengers on this flight will be people on they way to work, and many will be returning home the same day.

Departure SVG 6:40
Arrival BGO 7:15

Departure BGO 7:35
Arrival AES 8:20

Departure AES 8:40
Arrival TRD 9:25

For longer haul flights where the aircraft needs to be cleaned + catering and completely refueled, turnaround is usually 45 minutes. For example: Norwegian flight# D85874 from LPA - BGO, always operated with 737-800 with 186 seats (1-class). Flight time is 5 hours and 15 minutes and the aircraft have 45 minutes on the ground at BGO before returning to LPA as D85875 (5 hours and 30 minutes). By having a short ground stop, the same crew can return home without exceeding maximum allow duty time. This is a vacation flight to a sunny Canary Island, where nearly all passengers will have checked-in luggage and lots of carry-ons. Both front and rear doors will be used at BGO to speed things up.
 
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Re: Is there a minimum "rest" time for an aircraft?

Sat May 05, 2018 11:26 am

strfyr51 wrote:
That was what Airplane Model? And? What Airport?? The airplane didn't need either Fuel,Food, Nor potable water and probably didn't need a jetway.
no crew change, nor cabin refreshments. I won't call a BS but you'd be darn close to it. I worked airlines from 1980-2017 and I NEVER saw that quick of a turn. anyplace by anybody. especially in airline servce. What were you flying Beech 99's??


The aircraft was a 1900 so no autopilot, no fms, no potable water system, no lav, no galley, no cockpit door. The flight attendant was named Mr. Coleman and passengers were encouraged to come up to the cockpit to grab a paper cup and get water from Mr. Coleman if they wanted refreshments (water only)
https://goo.gl/images/axAc2p

The plane had airstairs installed in the door so was self sufficient no jetbridge. Passengers were off the airplane as soon as the FO could open the door. People usually couldn’t wait to get off the plane. No pushback tug was required except at two stations. (MDW and IAD)

Turns at the outstations were all scheduled for 10 minute turns at resorts / vacation / garden spots of Brookings SD, Visalia CA, Kingman AZ, Great Bend KS, Decatur IL, Watertown NY, Lancaster PA, Little Rock AR. Although Little Rock was the one station that could not turn the 1900 in anything less than one hour for that scheduled 10 minute turn.

Fueling time was the limiting factor since there was no fueling point. Fueling was overwing fueling. You could speed it up somewhat by landing with the maximum fuel imbalance and then fueling only the low wing (right wing) to the maximum fuel imbalance the other way.

But that is from a time gone era.
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pikachu
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Re: Is there a minimum "rest" time for an aircraft?

Sat May 05, 2018 11:53 am

Starlionblue wrote:
Brakes and engines as mentioned. Another limiting factor is fueling time, though that is more of an issue with widebodies.


Can somebody explain the minimum engine rest to me? A reference would be appreciated.
 
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Re: Is there a minimum "rest" time for an aircraft?

Sat May 05, 2018 5:05 pm

pikachu wrote:
Starlionblue wrote:
Brakes and engines as mentioned. Another limiting factor is fueling time, though that is more of an issue with widebodies.


Can somebody explain the minimum engine rest to me? A reference would be appreciated.


There are temperature limits for engine start. If the EGT temp is over the limit, you can't start it.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
mmo
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Re: Is there a minimum "rest" time for an aircraft?

Sat May 05, 2018 9:42 pm

Starlionblue wrote:
pikachu wrote:
Starlionblue wrote:
Brakes and engines as mentioned. Another limiting factor is fueling time, though that is more of an issue with widebodies.


Can somebody explain the minimum engine rest to me? A reference would be appreciated.


There are temperature limits for engine start. If the EGT temp is over the limit, you can't start it.


Isn't that what we motor the engine during start to ensure it is below 100C?
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e38
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Re: Is there a minimum "rest" time for an aircraft?

Sun May 06, 2018 12:11 am

Which aircraft have pre-start temperature limits?

e38
 
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Re: Is there a minimum "rest" time for an aircraft?

Sun May 06, 2018 3:59 am

e38 wrote:
Which aircraft have pre-start temperature limits?

e38


A330 (Trent) and A350 just to name two. 700C EFT limit for starting on the ground.


mmo wrote:
Starlionblue wrote:
pikachu wrote:

Can somebody explain the minimum engine rest to me? A reference would be appreciated.


There are temperature limits for engine start. If the EGT temp is over the limit, you can't start it.


Isn't that what we motor the engine during start to ensure it is below 100C?


The 350 automatically motors the engine if the temperature is high. However if the EGT is over 700 you're not permitted to start it.

I haven't paid attention to engine temperatures after shutdown though. Don't know how quickly they come down.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
pikachu
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Re: Is there a minimum "rest" time for an aircraft?

Sun May 06, 2018 12:12 pm

"The 350 automatically motors the engine if the temperature is high. However if the EGT is over 700 you're not permitted to start it."

If the EGT is over 700 degrees C on a shutdown engine I would suggest you have a bigger problem than not being able to start it.

Can anybody provide a manufacturer reference for this minimum engine rest phenomenon? A reference with the stated EGT would be appreciated.
 
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Starlionblue
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Re: Is there a minimum "rest" time for an aircraft?

Sun May 06, 2018 1:20 pm

pikachu wrote:
"The 350 automatically motors the engine if the temperature is high. However if the EGT is over 700 you're not permitted to start it."

If the EGT is over 700 degrees C on a shutdown engine I would suggest you have a bigger problem than not being able to start it.

Can anybody provide a manufacturer reference for this minimum engine rest phenomenon? A reference with the stated EGT would be appreciated.


Yes I agree that you would have a bigger problem. :) Nevertheless, the limits are there. Granted, most likely not a limitation on your typical turnaround.

FCOMs are proprietary but here's an older 330 FCOM. The EGT limits for this particular variant are on page 100. http://www.avialogs.com/en/aircraft/europe-and-consortiums/airbus/a330/airbus-330-fcom-flight-operations-volume-3.html#download
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
e38
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Re: Is there a minimum "rest" time for an aircraft?

Sun May 06, 2018 3:23 pm

Are the engine limitations you are making reference to imposed by Airbus, the engine manufacturer, or required by your airline? I am aware of the company for which you work and I know from time to time companies will specify additional systems limitations above and beyond those required by the manufacturer or component sub-contractor.

The reason I ask is that I was not previously aware of an engine temperature limitation prior to starting. The two aircraft I have flown most recently-one using Pratt and Whitney JT8D-17 engines and the other using CFM-56 engines-do not have such limitations.

e38
 
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Starlionblue
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Re: Is there a minimum "rest" time for an aircraft?

Sun May 06, 2018 3:48 pm

e38 wrote:
Are the engine limitations you are making reference to imposed by Airbus, the engine manufacturer, or required by your airline? I am aware of the company for which you work and I know from time to time companies will specify additional systems limitations above and beyond those required by the manufacturer or component sub-contractor.

The reason I ask is that I was not previously aware of an engine temperature limitation prior to starting. The two aircraft I have flown most recently-one using Pratt and Whitney JT8D-17 engines and the other using CFM-56 engines-do not have such limitations.

e38


It's in our FCOM for the aircraft. Thus by definition, it is imposed by my airline and our regulating authority. The original source is not known to me but I'm assuming Rolls-Royce since they make the engines.

The FCOM linked above, for the same aircraft, says LH, so it would seem we are not alone.

Also, again, the EGT limit is not really a limitation for a normal turnaround.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
mmo
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Re: Is there a minimum "rest" time for an aircraft?

Sun May 06, 2018 6:03 pm

pikachu wrote:
Can anybody provide a manufacturer reference for this minimum engine rest phenomenon? A reference with the stated EGT would be appreciated.


That was my point in my post. I haven't had anything to do with the 350, but up through the 787 there was none. The only real restriction was motoring the engine until the EGT was below 100C. Generally there was a pretty good temp drop when the engines were shutdown. So, if you had a high EGT remaining even with the engines motoring, you would have much greater problems to deal with.
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pikachu
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Re: Is there a minimum "rest" time for an aircraft?

Mon May 07, 2018 1:06 am

Starlionblue wrote:
pikachu wrote:
"The 350 automatically motors the engine if the temperature is high. However if the EGT is over 700 you're not permitted to start it."

If the EGT is over 700 degrees C on a shutdown engine I would suggest you have a bigger problem than not being able to start it.

Can anybody provide a manufacturer reference for this minimum engine rest phenomenon? A reference with the stated EGT would be appreciated.


Yes I agree that you would have a bigger problem. :) Nevertheless, the limits are there. Granted, most likely not a limitation on your typical turnaround.

FCOMs are proprietary but here's an older 330 FCOM. The EGT limits for this particular variant are on page 100. http://www.avialogs.com/en/aircraft/europe-and-consortiums/airbus/a330/airbus-330-fcom-flight-operations-volume-3.html#download


How are you interpreting this limitation? I see it as an upper EGT limit for a start attempt. How do you see it?

Image
 
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Starlionblue
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Re: Is there a minimum "rest" time for an aircraft?

Mon May 07, 2018 1:15 am

As you say an upper EGT limit for a start attempt. I never said there was a min engine rest. Just a max EGT.

Anyway, as I said above, it is unlikely that turnaround will be delayed due to high EGT.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
pikachu
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Re: Is there a minimum "rest" time for an aircraft?

Mon May 07, 2018 1:38 am

Starlionblue wrote:
As you say an upper EGT limit for a start attempt. I never said there was a min engine rest. Just a max EGT.

Anyway, as I said above, it is unlikely that turnaround will be delayed due to high EGT.


I think it would be a lot easier for everybody if you just posted the limitation that says thou shall not start an engine if EGT is over some value.
 
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Starlionblue
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Re: Is there a minimum "rest" time for an aircraft?

Mon May 07, 2018 2:46 am

pikachu wrote:
Starlionblue wrote:
As you say an upper EGT limit for a start attempt. I never said there was a min engine rest. Just a max EGT.

Anyway, as I said above, it is unlikely that turnaround will be delayed due to high EGT.


I think it would be a lot easier for everybody if you just posted the limitation that says thou shall not start an engine if EGT is over some value.


As you can see in the manual excerpt above the value is in the FCOM Limitations sections. "Don't exceed this value" is implied. That's the meaning of "limitations". Same as it doesn't say "don't start the engines if the oil quantity is below minimum" or "don't exceed the service ceiling".
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
pikachu
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Re: Is there a minimum "rest" time for an aircraft?

Mon May 07, 2018 4:18 am

Starlionblue wrote:
pikachu wrote:
Starlionblue wrote:
As you say an upper EGT limit for a start attempt. I never said there was a min engine rest. Just a max EGT.

Anyway, as I said above, it is unlikely that turnaround will be delayed due to high EGT.


I think it would be a lot easier for everybody if you just posted the limitation that says thou shall not start an engine if EGT is over some value.


As you can see in the manual excerpt above the value is in the FCOM Limitations sections. "Don't exceed this value" is implied. That's the meaning of "limitations". Same as it doesn't say "don't start the engines if the oil quantity is below minimum" or "don't exceed the service ceiling".


So if I understand correctly, if the EGT of an engine which is not running is above 535 degrees you must wait for it to cool down to 534 degrees or below before starting it?
 
mmo
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Re: Is there a minimum "rest" time for an aircraft?

Mon May 07, 2018 5:05 am

pikachu wrote:

So if I understand correctly, if the EGT of an engine which is not running is above 535 degrees you must wait for it to cool down to 534 degrees or below before starting it?



No. If you look at the top of the column, the condition is STARTING, not RESTING. A normal shutdown would never result in a 535C Temp if the engine had no problems. In fact, normal idle EGT would be well below the start limit. As soon as you begin the start sequence, the starter will begin to spin the engine which will take cool air into the inlet and through the engine and the temp will begin to decrease.

I hate to say it, but you are getting hung up on semantics. The only limit is, in this case 535C for a ground start. If you were a betting person, you could go up to 534.9C and be within limits.
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pikachu
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Re: Is there a minimum "rest" time for an aircraft?

Mon May 07, 2018 5:13 am

Hi thanks for your reply. I'm only hung up on the concept of a resting period for EGT something or other.

I understand the upper EGT limit quite well. It's the mystical "no you can't start the engine at that EGT limit because it needs to rest" that has me flummoxed.

In my experiences operating the JT8D, CF6, RB211, JT9D, GE90, PW4077, CFM56, and PW4060 I have yet to see a reference for the EGT cool down limit before starting.
 
mmo
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Re: Is there a minimum "rest" time for an aircraft?

Mon May 07, 2018 9:11 am

There is none! You have to be below 100C before moving the fuel lever to run. After that, the applicable start EGT limit will apply. That's it. Again, if you don't see a limit specified; there is none!
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pikachu
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Re: Is there a minimum "rest" time for an aircraft?

Mon May 07, 2018 12:07 pm

mmo wrote:
There is none! You have to be below 100C before moving the fuel lever to run. After that, the applicable start EGT limit will apply. That's it. Again, if you don't see a limit specified; there is none!


MMO thanks for the explanation! Please everybody pay attention to what he just said.
 
pikachu
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Re: Is there a minimum "rest" time for an aircraft?

Mon May 07, 2018 3:02 pm

Starlionblue wrote:
e38 wrote:
Which aircraft have pre-start temperature limits?

e38


A330 (Trent) and A350 just to name two. 700C EFT limit for starting on the ground.


mmo wrote:
Starlionblue wrote:

There are temperature limits for engine start. If the EGT temp is over the limit, you can't start it.


Isn't that what we motor the engine during start to ensure it is below 100C?


The 350 automatically motors the engine if the temperature is high. However if the EGT is over 700 you're not permitted to start it.

I haven't paid attention to engine temperatures after shutdown though. Don't know how quickly they come down.


Is it possible you have misinterpreted the EGT start limitation? See the bold part.

Is there a situation where you could envision an engine that is not running have an EGT over 700 degrees? If so I would appreciate your explanation as I just can't see a piece of equipment that is not operating having a temperature over 700 degrees.

As an aside, minimum engine oil is generally for dispatch, not engine starting. I have never seen a reference for "though shall not start engine if oil quantity is less than (whatever your company says)". No dispatch means the airplane doesn't go flying. No flying means no engine start. It's a long way from no dispatch to an engine start. So the implied limit you interpret is a bit shaky.

As a further aside, the maximum certified altitude of the aircraft is a hard value published in the AFM and FCOM Limitations section. You are absolutely correct in stating that nowhere does it say do not go above this altitude. However, I suppose the manufacturer has to take a chance that the people operating the aircraft are in possession of basic reading comprehension skills. And maybe a bit of applied understanding from time to time. So if a manufacturer states that a maximum certified altitude for airplane x is 43 100' what does that mean? Maximum certified altitude means that is the maximum altitude the manufacturer has decided they will certify the aircraft to operate at. This limitation is not implied. It is a published limitation.
 
mmo
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Re: Is there a minimum "rest" time for an aircraft?

Mon May 07, 2018 6:20 pm

pikachu wrote:
As a further aside, the maximum certified altitude of the aircraft is a hard value published in the AFM and FCOM Limitations section. You are absolutely correct in stating that nowhere does it say do not go above this altitude. However, I suppose the manufacturer has to take a chance that the people operating the aircraft are in possession of basic reading comprehension skills. And maybe a bit of applied understanding from time to time. So if a manufacturer states that a maximum certified altitude for airplane x is 43 100' what does that mean? Maximum certified altitude means that is the maximum altitude the manufacturer has decided they will certify the aircraft to operate at. This limitation is not implied. It is a published limitation.


Max certified altitude is the never exceed altitude. You never go above it. That altitude could be based on several issues. The most likely factor is the ability to descent from that altitude down to 14,000 in 4 minutes or less. However, it could be a aerodynamic limit or a thrust limit issue.
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Starlionblue
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Re: Is there a minimum "rest" time for an aircraft?

Tue May 08, 2018 1:03 am

As mmo said up-thread, we are getting hung up on semantics.

When I said the service ceiling limitation is "implied", I meant there is no phrase in the FCOM to the effect of "thou shalt never exceed this altitude". I didn't mean the limitations are not binding.

The manual just lists the various limitations. Notable exceptions are Vmo/Mmo, which come with the explicit warning "may not intentionally exceed".

Just as service ceiling is just a value, so is max EGT "starting". Neither comes with further instructions, and the EGT limit doesn't mention if it should be respected before start or during start. Again, though, a max EGT starting limitation is unlikely to impact turnarounds...
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pikachu
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Re: Is there a minimum "rest" time for an aircraft?

Tue May 08, 2018 2:32 am

Starlionblue wrote:

Neither comes with further instructions, and the EGT limit doesn't mention if it should be respected before start or during start. Again, though, a max EGT starting limitation is unlikely to impact turnarounds...


I mentioned above that if an engine that is not running has an EGT of over 700 degrees you have a more pressing issue than start considerations.

Do you really think the 700 degree limitation is for an engine which is not running?

I also mentioned the manufacturer relies on the operators of the airplanes to use some common sense and logic.

To conclude, there is no minimum rest period required for engines.
 
mmo
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Re: Is there a minimum "rest" time for an aircraft?

Tue May 08, 2018 6:19 am

To conclude there is no limitation for an engine which is not running!!! Again, semantics!
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lightsaber
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Re: Is there a minimum "rest" time for an aircraft?

Tue May 08, 2018 12:59 pm

Starlionblue wrote:
As mmo said up-thread, we are getting hung up on semantics.

When I said the service ceiling limitation is "implied", I meant there is no phrase in the FCOM to the effect of "thou shalt never exceed this altitude". I didn't mean the limitations are not binding.

The manual just lists the various limitations. Notable exceptions are Vmo/Mmo, which come with the explicit warning "may not intentionally exceed".

Just as service ceiling is just a value, so is max EGT "starting". Neither comes with further instructions, and the EGT limit doesn't mention if it should be respected before start or during start. Again, though, a max EGT starting limitation is unlikely to impact turnarounds...

As a test engineer with experience at setting both limits, let me discuss.

The EGT is just used as an indicator as much of what one cares about in engine cooling has no sensor and the regulating authorities like simple. So engine rotor bowing is quantified, roughly, by EGT. If lower than a number, the engine is safe to start.

Maximum altitude is set by a minimum climb rate at standard cruise speed. If the pilots have stall recovery training (much more training than standard commercial pilots), one can fly higher at high cruise speeds. This is why Air Force One can be above commercial traffic.

As rotors spn faster as compressor technology improves, the bearings are more susceptible to binding. So the EGT limit is lowered. The work around is to windmill the engine after engine shutdown.

Lightsaber

PS, late edit. Military versions of commercial aircraft need some changes to fly higher. For example, fans to ensure avionics will work in a cabin depressurization event. Extra testing to expand the cabin pressurization envelope. A different maintenance plan for the added stress of high altitude oos (greater pressure differential shortens maintenance intervals).

Military engines give up some efficiency and durability for higher EGT limits for start. There is an engineering trade for everything...
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windy95
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Re: Is there a minimum "rest" time for an aircraft?

Tue May 08, 2018 6:38 pm

neomax wrote:
Assuming a hypothetical scenario where turnaround, catering, fueling time is not a factor, is there such a thing as a required minimum "rest" time for an aircraft to spool down to idle and cool on the ground, or can it be sent back up as soon as it is ready?



There is no minimum rest time for aircraft.
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JayinKitsap
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Re: Is there a minimum "rest" time for an aircraft?

Tue May 08, 2018 7:48 pm

I think there may be an underlying question, the plane's stage length and turn around. Aloha stayed with the 737-200 on its inter island flights which some are less than 20 minutes in the air because the 300's and later because the CFM engines did not like the repeated short stage & turn around, the linked post notes lots of tech issues after 4 short stage flights in a day. A turbine at take off thrust really heats up, but the heat profile will be unbalanced, normal cruise returns this heat balance to a normal level so by the time it is back on the ground it is basically good to go.

viewtopic.php?f=3&t=387385&start=50

HA is still using 717-200's for its inter island, again as the engines deal with the short length high cycle conditions.
 
Apprentice
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Re: Is there a minimum "rest" time for an aircraft?

Tue May 15, 2018 9:17 am

Hi:
As previously noted, limited facors:
-brake temp. When brakes’ temp is high, brakes lost their capacity to disipate aircraft energy during taxi and /or on rejected T.O., specially on carbon fiber brakes. And that is a no-no. Brake temp before TO, is a limiting factor. Carbon brakes may be cold down only by air, by individuals’ brakes fan, or by mechanics using air hose (never water).
- high engine EGT. Due to differents materials and components, if Engine is not proper cold down (for instance, less than 100°C, very high vibration (out of limits) during engine start will take place,

Rgds
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