Airliner stall speed at cruising altitude
Discussion
It depends!
Which airliner?
What weight? What configuration? (Flaps / clean etc). An airliner with full fuel and a full passenger manifest will have a higher stall speed than an empty one.
From memory (so please don't quote me), I think the 'finals' speed is around 100 knots, so there will be a margin of error on that for stall speed and that will be with full flaps so doesn't really answer your cruise altitude (assuming clean airframe) question.
Someone more knowledgable than me will be along in a minute as there are airline pilots that post on here.
Which airliner?
What weight? What configuration? (Flaps / clean etc). An airliner with full fuel and a full passenger manifest will have a higher stall speed than an empty one.
From memory (so please don't quote me), I think the 'finals' speed is around 100 knots, so there will be a margin of error on that for stall speed and that will be with full flaps so doesn't really answer your cruise altitude (assuming clean airframe) question.
Someone more knowledgable than me will be along in a minute as there are airline pilots that post on here.
The higher you go, the higher the stall speed becomes.
The higher you go, the lower the maximum mach becomes....
What this means is that altitude becomes CRITICAL at some point. This is called the "coffin corner", where the allowable speed range for a particular airplane becomes very small. The B-47 bomber was NOTORIOUS because at the altitudes where it was fuel efficient, it had about a 5 knot spread between the two speeds!
The Boeing 757 at altitudes around FL400 at most weights has an INDICATED stall speed of between 220 and 230 knots. Remember now, indicated airspeed is completely different from true airspeed, which is the "500 knot" speed you mentioned. Typical indicated airspeed at that altitude is around 260 knots.
The higher you go, the lower the maximum mach becomes....
What this means is that altitude becomes CRITICAL at some point. This is called the "coffin corner", where the allowable speed range for a particular airplane becomes very small. The B-47 bomber was NOTORIOUS because at the altitudes where it was fuel efficient, it had about a 5 knot spread between the two speeds!
The Boeing 757 at altitudes around FL400 at most weights has an INDICATED stall speed of between 220 and 230 knots. Remember now, indicated airspeed is completely different from true airspeed, which is the "500 knot" speed you mentioned. Typical indicated airspeed at that altitude is around 260 knots.
Thanks, Normy, you have answered the question. As I thought, there is not a huge margin for error. All those "rock solid" feeling flights now seem rather more precarious than I recall.
And the question came from a discussion about AF447.
Subsidiary question:
Are aircraft being operated closer to design limits these days or has it always been thus?
And the question came from a discussion about AF447.
Subsidiary question:
Are aircraft being operated closer to design limits these days or has it always been thus?
Light weight aircraft and relatively low cruising altitudes give a huge performance spread with regards with speed. Min manouvering speed band is not even shown on the pfd. Angle of attack will be more limiting if you pull back quickly.
Oh and modern commercial aircraft and normally operated within 1.3Vs and in a manner which wouldn't put the aircraft near that under normal operations.
Oh and modern commercial aircraft and normally operated within 1.3Vs and in a manner which wouldn't put the aircraft near that under normal operations.
Edited by Kempus on Wednesday 9th December 15:19
Vs - Unloaded Stall Speed (ie unmanouevring stall speed).
1.3Vs is the minimum Vat (Velocity at Threshold [also known as Vref in some circles).
WRT 'Coffin Corner' - you don't go anywhere near there (unless you happen to be in something like a Canberra Pr9). What you do is you fly 'Height For Weight' which gives you a suitable buffet boundary margin for normal manoeuvre.
1.3Vs is the minimum Vat (Velocity at Threshold [also known as Vref in some circles).
WRT 'Coffin Corner' - you don't go anywhere near there (unless you happen to be in something like a Canberra Pr9). What you do is you fly 'Height For Weight' which gives you a suitable buffet boundary margin for normal manoeuvre.
On the subject of AF447 and a high altitude stall generally - in layman's terms - how 'easily' could this situation be rectified with the advantage of altitude? It is as simple as pointing the nose at the ground and regaining some speed or could you get well and truly 'stuck' in the stall? I've always wondered how simply the situation could have been recovered if the other pilots realised that matey boy had been pushing up, a little sooner.
Stall recovery at altitude has changed in recent years. Previously we were expected to 'power out' by giving it full thrust but trying to lose as little altitude as possible. After the Air France crash, this changed (on the B777 at least) so that we now sacrifice more altitude to increase the true airspeed over the wing quicker and this stabilise the stall. Get the plane slow enough however and you might not have enough power or elevator authority to get the nose down and recover.
I must admit that, as a QFI, we taught the Minimum Altitude Loss Recovery technique from any stall. Specifically 'unload, full power, then control the nose up pitch'. The reason being that a stall with a student is most likely to occur in the Visual Circuit (ie close to the ground) where your options are severly limited; the ground having a pK=1.
Having said that, I see no reason not to trade altitude for speed if you have it in hand.
However, only a bloody fool really allows his/her a/c (especially an airliner) to enter such a flight regime unintentionally. Possibly there is an argument for better 'General Handling' training for Civil pilots?
Having said that, I see no reason not to trade altitude for speed if you have it in hand.
However, only a bloody fool really allows his/her a/c (especially an airliner) to enter such a flight regime unintentionally. Possibly there is an argument for better 'General Handling' training for Civil pilots?
theboss said:
On the subject of AF447 and a high altitude stall generally - in layman's terms - how 'easily' could this situation be rectified with the advantage of altitude? It is as simple as pointing the nose at the ground and regaining some speed or could you get well and truly 'stuck' in the stall? I've always wondered how simply the situation could have been recovered if the other pilots realised that matey boy had been pushing up, a little sooner.
I believe the report into AF447 showed that the stall became effectively un-recoverable after a time period, because the HS autotrim wound in during the time the pilots were continuously pulling back. Hence had they ever pushed forwards, by the time enough trim had come off to pull the aircraft out of the deep stall, they would have run out of sky..........The difference of course is that you have a lot more residual thrust at low altitude, so powering out whilst losing less height to avoid terrain would be preferable.
My company has realised that as pilots we don't hand fly as much as we should. I'm typing this just about to go into a manual handling simulator session which we do typically every 6 months. Here we'll be practising many manoeuvres that we might never (hopefully) have to do for real, such as stalls, tcas events and engine failures.
My company has realised that as pilots we don't hand fly as much as we should. I'm typing this just about to go into a manual handling simulator session which we do typically every 6 months. Here we'll be practising many manoeuvres that we might never (hopefully) have to do for real, such as stalls, tcas events and engine failures.
Thanks for answering the question guys (and girls) 
So essentially it could most likely have been rescued early on but once in a deep stall and fast losing altitude they soon ran out of options... pretty much as I thought.
The thing which puzzles me is how they lost all their bearings and seemingly became fixated on the erroneous speed indications but seemed to read the altimeter at 10,000ft without too great a concern. Who knows what was going through their minds in those fatal last minutes.
So essentially it could most likely have been rescued early on but once in a deep stall and fast losing altitude they soon ran out of options... pretty much as I thought.
The thing which puzzles me is how they lost all their bearings and seemingly became fixated on the erroneous speed indications but seemed to read the altimeter at 10,000ft without too great a concern. Who knows what was going through their minds in those fatal last minutes.
Ginetta G15 Girl said:
Vat is what you 'come over the fence at', touchdown speed is 5-10 Kts less than Vat.
Thanks! At the end of the day it's all air over bits of metal isn't it Ginetta G15 Girl said:
However, only a bloody fool really allows his/her a/c (especially an airliner) to enter such a flight regime unintentionally. Possibly there is an argument for better 'General Handling' training for Civil pilots?
Whilst not a pilot (well only in a forthcoming film but that's another story), I think the further you isolate the pilot/s from reality - which is what they're flying in - the more likely things are to go wrong when they go wrong.theboss said:
The thing which puzzles me is how they lost all their bearings and seemingly became fixated on the erroneous speed indications but seemed to read the altimeter at 10,000ft without too great a concern. Who knows what was going through their minds in those fatal last minutes.
Easy to be wise after the event, but with visual reference gone, trusted instruments gone and 'seat of the pants' also gone due to the capriciousness of G, Newton is the favourite to win.I appreciate the comments about low level stalls and have a good understanding and feel for that. I'm still not entirely sure I have the full information I seek for typical airline cruising heights.
Normy said:
The Boeing 757 at altitudes around FL400 at most weights has an INDICATED stall speed of between 220 and 230 knots. Remember now, indicated airspeed is completely different from true airspeed, which is the "500 knot" speed you mentioned. Typical indicated airspeed at that altitude is around 260 knots.
(260-230) / 230 = 13% margin. Or, in layman's terms, "not much" margin for error. Has it ever been thus or are airliners being operated closer to the limit than in earlier decades?Gassing Station | Boats, Planes & Trains | Top of Page | What's New | My Stuff