Is there any daily limit of the hours one aircraft can fly within 24 hours, for example, can a plane make a 10 hour to some place and then return for more 10 hours within 24 hours?

greetings from Brazil !!!!

There have been aircraft used for 17+ hours in a 24 time period.
It comes down to turn times. Most new aircraft can go days between inspections thanks to sensor feedback.
The more time on the ground, the fewer flight hours.
For narrowbodies, about 16 hours per day is the highest I've seen by JetBlue (B6) flying TCON, 3 missions per day per aircraft.

The older an aircraft, the more maintenance time it needs. Thus, they will fly fewer hours.
New aircraft require an "A check" about every 850 flight hours, so that will have to be scheduled in.

Aircraft engine oil is treated between oil changes, so engine down time is short. In fact, oil filter replacement is routine maintenance (no oil change typically, just the filter). Engines stay on wing for 20,000 cycles (narrowbodies), and for extended times (30,000+ hours on a widebody).

Lightsaber

Aircraft leases (new or young - under 12, and certain types of financing) include total hours and cycles, which may in turn be expressed as annual values. Hours / cycle values may not be included for older aircraft, as maintenance tends to provide a natural cap.

Hours and/or cycles in excess of agreed values trigger additional payments, sometimes collected in the final balloon payment (at end of lease), or depending on the assessed credit risk of the leasee, annually or even monthly.

Agreed values for air frames and engines are usually the same, but not always.

OEM lifetime hours and cycle extensions are not usually passed on to the leasee. They may be used as a 'carrot' at end of lease negotiations, to encourage a follow on lease (or sale of the aircraft to the leasee).

lightsaber wrote:

There have been aircraft used for 17+ hours in a 24 time period.
It comes down to turn times. Most new aircraft can go days between inspections thanks to sensor feedback.
The more time on the ground, the fewer flight hours.
For narrowbodies, about 16 hours per day is the highest I've seen by JetBlue (B6) flying TCON, 3 missions per day per aircraft.

The older an aircraft, the more maintenance time it needs. Thus, they will fly fewer hours.
New aircraft require an "A check" about every 850 flight hours, so that will have to be scheduled in.

Aircraft engine oil is treated between oil changes, so engine down time is short. In fact, oil filter replacement is routine maintenance (no oil change typically, just the filter). Engines stay on wing for 20,000 cycles (narrowbodies), and for extended times (30,000+ hours on a widebody).

Lightsaber

Could you explain a bit more on the engine oil changes? As an outsider, I had assumed engines were an attrition type system where fresh oil is added when needed and the used oil basically goes out the tailpipe so there is never any truly "old" oil in there. Just change the filter and top off the reservoir.

Spacepope wrote:

lightsaber wrote:

There have been aircraft used for 17+ hours in a 24 time period.
It comes down to turn times. Most new aircraft can go days between inspections thanks to sensor feedback.
The more time on the ground, the fewer flight hours.
For narrowbodies, about 16 hours per day is the highest I've seen by JetBlue (B6) flying TCON, 3 missions per day per aircraft.

The older an aircraft, the more maintenance time it needs. Thus, they will fly fewer hours.
New aircraft require an "A check" about every 850 flight hours, so that will have to be scheduled in.

Aircraft engine oil is treated between oil changes, so engine down time is short. In fact, oil filter replacement is routine maintenance (no oil change typically, just the filter). Engines stay on wing for 20,000 cycles (narrowbodies), and for extended times (30,000+ hours on a widebody).

Lightsaber

Could you explain a bit more on the engine oil changes? As an outsider, I had assumed engines were an attrition type system where fresh oil is added when needed and the used oil basically goes out the tailpipe so there is never any truly "old" oil in there. Just change the filter and top off the reservoir.

That is correct - it is typically a top off system.
The filter is changed regularly.
The only time you get a full oil change is for maintenance - typically doing a calibration check of the indication system.
Other then that - top it off and go.

but so, is it or not possible to use an aircraft 20 hours within 24 hours?

LPSHobby wrote:

but so, is it or not possible to use an aircraft 20 hours within 24 hours?

In all the years on a.nut I've not seen a reason why it couldn't be used 20 hours in 24. Or even 23 hours, if the crew - and its replacement - sleeps aboard, has additional fuel tanks installed, has zero payload, and gets priority at every landing, and uses additional pumps to fuel her up...

Technically, much is possible. But from an operational point of view... you need time for refuelling, passengers need to leave and find their seats, baggage, and then some reserve for unforeseen delays. You don't want the Sunday delays to creep into Monday, and then they creep further into Tuesday...

If a plane gets used 20 hours a day, and it gets 30 minutes of daily delays (which are hard to compensate in these 4 hours), the plane will be 7.6 days late after a year.


David

LPSHobby wrote:

but so, is it or not possible to use an aircraft 20 hours within 24 hours?

Of course it is - just think of it from a basic scheduling principle. For example, a flight from the middle east to west coast US 16:20hr outbound and 15:50hr inbound with a minimum turn around time in the outstation - based on an 0500 departure and 1500 arrival on the return time that's 32hrs of flying in a 34hr period

LPSHobby wrote:

but so, is it or not possible to use an aircraft 20 hours within 24 hours?

Absolutely possible. It actually happens too for a limited stretch. Rarely do planes fly that much for more than 3 consecutive days since they need maintenance ground time.

UA has a 767 Fly EWR-HNL-EWR. It is blocked at 20.5 hours of flying within a 24 hour period with 100 minutes in EWR and 110 minutes in HNL ground time. It is common for the same plane to fly to HNL for two or three days in a row. UA also has some 737s flying 36-38 hours in a 48 hour period with some transcon Redeyes or Hawaii turns.

Flying too many hours in a short period of time results in a number of deferred maintenance items. Without enough time to clear them, there are risks of delays down the line.

Most narrowbodies average 9-14 hours of utilization a day. Widebodies are a bit higher in the 10-16 hour range including all the maintenance time.

The various militaries have flown planes for 24+ hours in a row. The RAF’s Hercs flew something 28 hours from Acension to Port Stanley and return. About 12 C-5s ran for 28+ hours—SAV-MGQ-CAI back in the 90s rescuing Les Aspin’s folly.

The bombers have all done 30+ hour combat or training missions numerous times.

GF

Spacepope wrote:

lightsaber wrote:

There have been aircraft used for 17+ hours in a 24 time period.
It comes down to turn times. Most new aircraft can go days between inspections thanks to sensor feedback.
The more time on the ground, the fewer flight hours.
For narrowbodies, about 16 hours per day is the highest I've seen by JetBlue (B6) flying TCON, 3 missions per day per aircraft.

The older an aircraft, the more maintenance time it needs. Thus, they will fly fewer hours.
New aircraft require an "A check" about every 850 flight hours, so that will have to be scheduled in.

Aircraft engine oil is treated between oil changes, so engine down time is short. In fact, oil filter replacement is routine maintenance (no oil change typically, just the filter). Engines stay on wing for 20,000 cycles (narrowbodies), and for extended times (30,000+ hours on a widebody).

Lightsaber

Could you explain a bit more on the engine oil changes? As an outsider, I had assumed engines were an attrition type system where fresh oil is added when needed and the used oil basically goes out the tailpipe so there is never any truly "old" oil in there. Just change the filter and top off the reservoir.

That's very true. Oil consumption is monitored closely. Especially on an ETOPS airplane.( or EROPS as some call itr now). Oil consumption is trend monitired and above a predetermined level the engine has to be troubleshot for high Oil consumption up to and including replacing the engine if Necessary. I can't imagine any airline that doesn't track their engine's oil consumption. (At least in the USA)

You can fly your plane for as long as you want, remembering that every x hours it requires a hangar visit for maintenance which depends on the type of maintenance scheduling the airline uses. In SAA's case we flew most of our flights between 05:00 to 23:00 with a red eye in between. From 23:00 the aircraft would go to the hangar for btx's or terminals or phase A's - just dependent on the logbook hours flown. I think they term the checks differently these days but the btx or base transit check was done at the end of each day on return to base, the terminal check was say every 45 hours and the phase A every 125 hours. If an aircraft stayed away from base the line station would do a line transit check. If it was the first flight of the day every aircraft undergoes a pre-flight check. These checks were basically a single sheet check and signed off in the technical log, whereas the higher checks were detailed and signed off on computer generated sheets. Our A300's for instance flew non stop JNB-DUR or JNB-CPT with the odd flight over border with the crews rotating.

Engine oil never gets changed unless contaminated or as mentioned a calibration check is carried out. The engines continuously consume oil and I remember the old B747's would take about 20 to 24 quarts after the long flights around the Bulge of Africa.

LPSHobby wrote:

but so, is it or not possible to use an aircraft 20 hours within 24 hours?

We do it occasionally for example. HKG-JFK-HKG-SYD aircraft might only spend less than 7 hrs on the ground in 2 days.

AY does 24h rotations on most of their long hauls. This means the same plane departs to Asia in the afternoon Finnish time, does the turn around in the morning and flies back so that it is again ready to depart in the following afternoon. This often results in 20+h utilization and is a major competetive point for them in terms of fleet utilization.

Here's an example: https://www.flightradar24.com/data/aircraft/oh-ltm

As long as you can keep fuel in the aircraft and oil in the engines, there is no mechanical reason an aircraft can't fly for well over 24 hours. There are no built in mechanical time limits. Now, from a legal point of view, some maintenance items aren't allowed to "drop-dead" in the air. These tend to be hour-driven checks and AD driven type things, but operators have different requirements.

Of course, things may break in flight that require the aircraft land.

Balerit wrote:

Engine oil never gets changed unless contaminated or as mentioned a calibration check is carried out. The engines continuously consume oil and I remember the old B747's would take about 20 to 24 quarts after the long flights around the Bulge of Africa.

Sorry to drag this up but it's fascinating. Is that engine oil use per engine or the total of all 4 for the flight?

Spacepope wrote:

Balerit wrote:

Engine oil never gets changed unless contaminated or as mentioned a calibration check is carried out. The engines continuously consume oil and I remember the old B747's would take about 20 to 24 quarts after the long flights around the Bulge of Africa.

Sorry to drag this up but it's fascinating. Is that engine oil use per engine or the total of all 4 for the flight?

Per engine but it varied from engine to engine.

Spacepope wrote:

Balerit wrote:

Engine oil never gets changed unless contaminated or as mentioned a calibration check is carried out. The engines continuously consume oil and I remember the old B747's would take about 20 to 24 quarts after the long flights around the Bulge of Africa.

Sorry to drag this up but it's fascinating. Is that engine oil use per engine or the total of all 4 for the flight?

I just want to correct a mistake I made where I wrote quarts; it should be pints or 10 to 12 quarts.

Balerit wrote:

Spacepope wrote:

Balerit wrote:

Engine oil never gets changed unless contaminated or as mentioned a calibration check is carried out. The engines continuously consume oil and I remember the old B747's would take about 20 to 24 quarts after the long flights around the Bulge of Africa.

Sorry to drag this up but it's fascinating. Is that engine oil use per engine or the total of all 4 for the flight?

I just want to correct a mistake I made where I wrote quarts; it should be pints or 10 to 12 quarts.

Thanks, still fascinating. These turbines got nothing on the oil consumption of the old big radials though.

Spacepope wrote:

Thanks, still fascinating. These turbines got nothing on the oil consumption of the old big radials though.

There's an old saying we had about the JT9-7XX, if it wasn't wet, it was out of oil. The things leaked it and burned it at an astonishing rate. Our oil consumption limit, if you can call it that, for dispatch, was interesting. We needed to ensure, based on the calculated, current consumption that the engine would arrive at its planned destination with at least 4 quarts remaining. Of course, we started looking at the engine long before that limit was actually reached.

Modern turbines can go hours without taking a pint of oil. The grounding limit, for all intents and purposes, on our CF6 engines is .55 quarts/hr. We restrict from ETOPS at .3pints/hr.

I think this must be happening regularly.

Back in the 90's, i had the opportunity to look at the scheduling of a major carrier flying A320's. Noticed their planes were scheduled in A-B pairs each flying 18-22 hours a day - plane A operates a certain set of routes on Day 1 and on Day 2 operates flights operated by plane B the previous day and vice versa.

This should have pushed their utilization averages higher - but with 4 out of 27 A320's (their fleet size then) in various maintenance checks at any time, the overall averages were a more realistic 12 hours/day.

Airplanes don't need rest. You need to keep them serviced and have a reason for them to fly.

7673mech wrote:

Spacepope wrote:

lightsaber wrote:

There have been aircraft used for 17+ hours in a 24 time period.
It comes down to turn times. Most new aircraft can go days between inspections thanks to sensor feedback.
The more time on the ground, the fewer flight hours.
For narrowbodies, about 16 hours per day is the highest I've seen by JetBlue (B6) flying TCON, 3 missions per day per aircraft.

The older an aircraft, the more maintenance time it needs. Thus, they will fly fewer hours.
New aircraft require an "A check" about every 850 flight hours, so that will have to be scheduled in.

Aircraft engine oil is treated between oil changes, so engine down time is short. In fact, oil filter replacement is routine maintenance (no oil change typically, just the filter). Engines stay on wing for 20,000 cycles (narrowbodies), and for extended times (30,000+ hours on a widebody).

Lightsaber

Could you explain a bit more on the engine oil changes? As an outsider, I had assumed engines were an attrition type system where fresh oil is added when needed and the used oil basically goes out the tailpipe so there is never any truly "old" oil in there. Just change the filter and top off the reservoir.

That is correct - it is typically a top off system.
The filter is changed regularly.
The only time you get a full oil change is for maintenance - typically doing a calibration check of the indication system.
Other then that - top it off and go.

Not only top it off and go. The oil in the filters is sampled. If an oil compound is low, another blend might be added.

But if there is concern, at the next A check out can be changed. However, that isn't very common. With the acid treatments... I'll admit I've lost track of how long.

Lightsaber

fr8mech wrote:

As long as you can keep fuel in the aircraft and oil in the engines, there is no mechanical reason an aircraft can't fly for well over 24 hours. There are no built in mechanical time limits. Now, from a legal point of view, some maintenance items aren't allowed to "drop-dead" in the air. These tend to be hour-driven checks and AD driven type things, but operators have different requirements.

Of course, things may break in flight that require the aircraft land.

Most engines have a 72 hour flight limit before the oil must be treated (which might be a top off only). That is, 72 flight hours.

So one can fly 72 hours theoretically with air to air refueling.

fr8mech wrote:

Spacepope wrote:

Thanks, still fascinating. These turbines got nothing on the oil consumption of the old big radials though.

There's an old saying we had about the JT9-7XX, if it wasn't wet, it was out of oil. The things leaked it and burned it at an astonishing rate. Our oil consumption limit, if you can call it that, for dispatch, was interesting. We needed to ensure, based on the calculated, current consumption that the engine would arrive at its planned destination with at least 4 quarts remaining. Of course, we started looking at the engine long before that limit was actually reached.

Modern turbines can go hours without taking a pint of oil. The grounding limit, for all intents and purposes, on our CF6 engines is .55 quarts/hr. We restrict from ETOPS at .3pints/hr.

Haha... We used to put cookie sheets underneath.

lightsaber wrote:

7673mech wrote:

Spacepope wrote:

Could you explain a bit more on the engine oil changes? As an outsider, I had assumed engines were an attrition type system where fresh oil is added when needed and the used oil basically goes out the tailpipe so there is never any truly "old" oil in there. Just change the filter and top off the reservoir.

That is correct - it is typically a top off system.
The filter is changed regularly.
The only time you get a full oil change is for maintenance - typically doing a calibration check of the indication system.
Other then that - top it off and go.

Not only top it off and go. The oil in the filters is sampled. If an oil compound is low, another blend might be added.

But if there is concern, at the next A check out can be changed. However, that isn't very common. With the acid treatments... I'll admit I've lost track of how long.

Lightsaber

Not saying it's impossible - never seen oil treated.
We cut filters open, send oil samples out, but rare that anything comes back abnormal.

I think we all agree going to the original question, basic servicing aside, loading and unloading, etc. there is no limit on how long they can fly.

NZ and SQ regularly use the Same frame AKL-SIN-AKL for several days, this means the aircraft is in the air close to 20hrs in a 24 hr period, NZ is a 789 while SQ do it with A380’s/77W’s.

lightsaber wrote:

Most engines have a 72 hour flight limit before the oil must be treated (which might be a top off only).

I've never seen or heard of that limit. Of course, that's academic, because the chances of any engine operating for 72 hours is just about zero.

At about 28 hours of run time, a couple of our GE TF-39 engines on the C-5 were running low oil quantity. Pulled to idle on descent into Cairo West, low oil pressure lights and indication.

GF