JAGflyer
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Older aircraft and uneven thrust level positions

Thu Nov 09, 2017 5:34 pm

I have noticed that on some of the older jet aircraft (707, 727, 747-100/200, and DC-8 for example) it is common to see the flight engineer adjusting the thrust levers unevenly. A pilot who had flown the 727 explained to me that this is done as older engines/aircraft without digital engine control required crews to manually sync up the "EPR" (or EPPR?) values. Basically, each engine was individually controlled and there was no centralized computer which would automatically even out various parameters to ensure all engines were giving the same output. Perhaps someone here can explain this idea to me a bit more clearly.
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Lpbri
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Re: Older aircraft and uneven thrust level positions

Thu Nov 09, 2017 7:03 pm

If an older A/C like you mentioned is trimmed properly, you should have no throttle stagger. On an MD-80 you are allowed a 1/2 knob split. I don't know about the others, but an MD-80 has an EPR synch function, so no manual adjustment is required.
 
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Balerit
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Re: Older aircraft and uneven thrust level positions

Thu Nov 09, 2017 8:38 pm

Yip, those older aircraft suffered from throttle stagger from time to time. As engines deteriorate so they start losing power hence the need to advance the throttle lever and as Lpbri says, half a knob is the limit. One could take the aircraft for a ground run and trim the fcu back into the power band however it was possible on the B747 -200's to have a little trimming tool made and manually turn it a certain amount of clicks but a tight record had to be made of how many clicks were done.
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Redbellyguppy
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Re: Older aircraft and uneven thrust level positions

Thu Nov 09, 2017 8:43 pm

Engine wear and fuel control unit notwithstanding... in these older airplanes there was a physical cable out to the engine. They stretch and wear unevenly.
 
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Starlionblue
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Re: Older aircraft and uneven thrust level positions

Fri Nov 10, 2017 1:40 am

In simple terms, nowadays FADEC does the adjusting for you to ensure the engines are producing the same thrust. This may result in uneven fuel flow between the engines.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
fr8mech
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Re: Older aircraft and uneven thrust level positions

Fri Nov 10, 2017 1:59 am

On the B747-100/200 the limit was 1/2 knob with no action and up to 1 knob with a deferral. In order to minimize throttle stagger, we would hang the trim equipment on all the engines after an engine change and bring all 4 engines into trim/rig. As stated, sometimes it's a cable issue, sometimes an engine issue.
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Balerit
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Re: Older aircraft and uneven thrust level positions

Fri Nov 10, 2017 1:59 pm

Cables should never be an issue, they would get changed. Also don't forget the AIDS sensor is located in the strut of the B747 on the teleflex cable and would give erroneous readings if the cables were stretched.
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VSMUT
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Re: Older aircraft and uneven thrust level positions

Fri Nov 10, 2017 5:43 pm

Balerit wrote:
Cables should never be an issue, they would get changed. Also don't forget the AIDS sensor is located in the strut of the B747 on the teleflex cable and would give erroneous readings if the cables were stretched.


Cables are the issue on the ATR, especially older ones. The cables get worn out, or slip where they are connected to the power levers, I'm not exactly sure, but the power lever position does deteriorate over time. The mechanics usually fix it pretty fast once notified, but again, they only have whatever details the pilots give them. Sometimes you find an aircraft with power levers completely out of whack because a crew told them to adjust the wrong lever. Same goes for the condition levers, and sometimes the CLs cant even be set to 77% due to this.
 
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Balerit
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Re: Older aircraft and uneven thrust level positions

Fri Nov 10, 2017 7:03 pm

Cables are rigged using rigging pins and tensiometers, it's not possible to have faulty cables unless your maintenance is non existent. There is no force on the cables anyway, not like control surface cables that have lots of load. On the old B747's there are friction clutches on the throttle levers themselves to prevent unscheduled movement. If the condition levers aren't rigged properly you'll get incorrect starts, as they schedule the fuel and the ignition. These ATR's sound dodgy to me.
Licensed Aircraft Maintenance Engineer (retired).
 
Lpbri
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Re: Older aircraft and uneven thrust level positions

Fri Nov 10, 2017 7:21 pm

A throttle rig is usually performed prior to engine trimming. Its not that hard. You dont mess with the cables. As was said, they not under a lot of tension. Adjustments are made with rig pins installed and adjusting rod ends for a slip fit of the bolts and aligning slots on the throttle spindle for idle, max power and reverse.
 
Max Q
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Re: Older aircraft and uneven thrust level positions

Sat Nov 11, 2017 12:07 am

Lpbri wrote:
If an older A/C like you mentioned is trimmed properly, you should have no throttle stagger. On an MD-80 you are allowed a 1/2 knob split. I don't know about the others, but an MD-80 has an EPR synch function, so no manual adjustment is required.



I spent four years flying the MD80, we had
Various sub types in a fleet of over 60 but
I never saw one with EPR synch

N1 or N2 synch was fitted, activated with
a switch on the overhead
The best contribution to safety is a competent Pilot.
 
JAGflyer
Topic Author
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Re: Older aircraft and uneven thrust level positions

Sat Nov 11, 2017 12:21 am

Here is a video of a 747-200 at departure which shows what I am talking about. https://www.youtube.com/watch?v=2KreKVGomZQ
If you flew today, thank a Flight Dispatcher!
 
Lpbri
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Re: Older aircraft and uneven thrust level positions

Sat Nov 11, 2017 4:02 am

The ERP sych is an auto throttle function. If the assumed temp is entered, auto throttle armed, and EPR lim button pushed, EPR sych is activated. It's all on the TRI.
 
Max Q
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Re: Older aircraft and uneven thrust level positions

Sun Nov 12, 2017 9:34 am

Lpbri wrote:
The ERP sych is an auto throttle function. If the assumed temp is entered, auto throttle armed, and EPR lim button pushed, EPR sych is activated. It's all on the TRI.



Interesting, did not know the TRI
incorporated that feature, especially
considering how crude the autothrottle
response was on the-80

Unless you were in perf mode it was
very rough
The best contribution to safety is a competent Pilot.
 
DashTrash
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Re: Older aircraft and uneven thrust level positions

Tue Nov 14, 2017 6:02 pm

Starlionblue wrote:
In simple terms, nowadays FADEC does the adjusting for you to ensure the engines are producing the same thrust. This may result in uneven fuel flow between the engines.

Even with FADEC you may have a little stagger to sync the engines. I'm flying near factory new aircraft right now with automatic engine sync above a certain N1. With the sync on the thrust levers are dead nuts even. When we're at power settings below the auto sync we may have to manually sync causing a little split. It's very little, however, nothing like the older jets and turboprops I flew.
 
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Starlionblue
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Re: Older aircraft and uneven thrust level positions

Wed Nov 15, 2017 12:38 am

DashTrash wrote:
Starlionblue wrote:
In simple terms, nowadays FADEC does the adjusting for you to ensure the engines are producing the same thrust. This may result in uneven fuel flow between the engines.

Even with FADEC you may have a little stagger to sync the engines. I'm flying near factory new aircraft right now with automatic engine sync above a certain N1. With the sync on the thrust levers are dead nuts even. When we're at power settings below the auto sync we may have to manually sync causing a little split. It's very little, however, nothing like the older jets and turboprops I flew.


This is where I point out that I fly Airbus. If the levers aren't both in the CLB detent during the cruise something is wrong. :D
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo

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