Any aircraft with ADCs usually display EAS actually, which is the IAS corrected for position, error and compressibility. The speed you see on the PFD is actually CAS/EAS, not IAS.Besides - I can't see what relevance that has - it is still measuring pressure sensed at the pitot head.

They don't display EAS. They usually display CAS, and in stby ASIs raw IAS is displayed. The point was the increase of indicated airspeed and the decrease of AoA in high altitudes. I specifically mentioned that when IAS (or CAS for that matter, doesn't matter, as long as compressibility error is still inside the displayed speed) is the reference, flying high altitude will show an increase in the IAS/CAS vs. EAS/TAS due to compressibility. This is the other big contributor to the scenario, where you will see a jet stall at a higher IAS (or CAS in the case of Airbus/Boeing) than if you were flying at a lower altitude.

Source? Nowhere in the lift equation do I see weight/mass as a variable.

See: http://www.grc.nasa....ane/airsim.html and http://www.grc.nasa....plane/mach.html(bold emphasis mine)"But for high speeds, some of the energy of the object goes into compressing the fluid and changing the density, which alters the amount of resulting force on the object.""This compressibility effect alters the amount of resulting force on the aircraft." And... Ace the Technical Pilot Interview - Google Books (page 28)And... http://home.anadolu.edu.tr/~mcavcar/hyo301/16_CompressibilityEffects.pdf (page 4)Essentially, what it means is that the compressibility drag is increased when spd above critical mach number. Thus causing a stall on a higher speed than what would happen, if all the airfoil parts were subsonic. Tero

Great link!A question though: why does this result in reduced stall alpha? You increase AoA, you increase the lift generated. Whilst compressibility reduces the lift generated, and so the aircraft has a higher stalling speed (that is very clear), it doesn't adequately explain why the stall alpha reduces (assume infinite thrust is available to overcome drag). Unless I'm blind and failing to see the relationship...Best regards,Robin.

Great link!A question though: why does this result in reduced stall alpha? You increase AoA, you increase the lift generated. Whilst compressibility reduces the lift generated, and so the aircraft has a higher stalling speed (that is very clear), it doesn't adequately explain why the stall alpha reduces (assume infinite thrust is available to overcome drag). Unless I'm blind and failing to see the relationship...

Robin,Here's the simple answer: http://www.av8n.com/...html#sec-cl-aoaIn short: whenever the critical angle of attack is reduced, the speed at which the critical aoa is met, must increase. And similarly, if the stall speed increases due to compressibility, it means that the critical angle of attack is reached ealier, ie, at a smaller angle. The two are always linked with any given coefficient of lift.Tero

To your list one might add several of the 737 stalls noted here - http://www.b737.org....ent_reports.htm - such as Algiers in 2003, Nigeria in 2005 and it's not just a third world thing either: see for example Pittsburgh, PA in 1994, Washington, DC in 1982 and Chicago Midway in 1972, where stall was also a factor.As I understand it, the training of commercial airline pilots concentrates on the approach to stall but leaves trainees relatively unexposed to the stall regime itself. Both of them are fundamental risk areas in real life yet, according to some of the posts at pprune to which I referred previously, the second of them in particular tends to be neglected (no doubt, relatively rather than absolutely) or imperfectly understood.I would have thought that simulator accuracy both in the approach to stall and in the stall regime itself is far more important than many of the arcane details with which the NGX is apparently replete, such as which bus supplies electricity to which light bulb and other details far removed from the "critical path" of safety. So I am sure that PMDG will want to model the stall behaviour as accurately as they can within the limits of what is achievable under FSX.I am sorry if the above sounds "off-topic" but I think the OP raised an interesting point which has not been answered yet. People use FSX with different priorities in terms of fidelity of experience. My own perspective is that FSX when combined with high-fidelity products such as PMDG's, is mainly educational as it engages with a wider interest in airline safety. Understanding the limits of the fidelity ESPECIALLY at and beyond the margins of the aeroplane's normal performance envelope, is therefore of interest, IMHO.Tim

Thanks Tim, you quoted: "I am sorry if the above sounds "off-topic" but I think the OP raised an interesting point which has not been answered yet." I also am wondering if PMDG might have possilbly added a line or two addressing this issue of FSX aerodynamic limitiations and whether or not they in fact addressed some of these limitations. I know that they did mention the aerodynamic float characteristics during the landing phase so they have done some modifications to FSX but was curious if they made other seemingly important mods to these particular files. Regards, jen noulet

In case this is of interest to anyone, this training for stall issue actually seems to be a pretty serious one. This airline pilot says he has had no training for stall recovery since his first type:http://www.pprune.org/tech-log/454676-stalling-airliner.html#post6516140Tim

This is because the training emphasis nowadays is on avoiding a stall rather than how to get out of one if you do actually stall. I recall being very vocal in complaining about that in a few real-world aviation magazines some years ago when they made those changes to the JAR rules, changes which included not bothering to teach people how to recover from a spin. I wrote many letters about it, but it was all for nothing.It is all very well teaching people not to get into a stall or spin, but that's no help if you actually do get into one. Anyone who knows their history will be aware that way back at the dawn of aviation, literally hundreds of pilots were killed on the Sopwith Camel simply because they did not know how to recover from a spin. It might be somewhat forgivable that this was the case back when aviation was in its infancy and people were being rushed through pilot training to fight in a war, but even so, many of those fatalities could so easily have been avoided.So to me it is shameful that the authorities would consider it not important for a pilot to know how to do recover from a spin when they know for a fact that it has led to many deaths, and not just in old WW1 biplanes. The other really ironic thing, is that stalling and spinning an aeroplane is actually bloody good fun, so it seems such a shame that many pilots will miss out on doing it.Of course for training that in an airliner, you'd need a simulator that could reproduce a stall or spin in a manner similar to the real aeroplane, and you'd probably not want to use a real airliner for it, but even so, it wouldn't hurt to get line pilots up in a smaller aircraft once in a while and get them to do a few stall and spin recoveries, after all, they have a big responsibility, with potentially hundreds of lives in their hands, so their skills should really be as up to scratch as they can be.Al

... I recall being very vocal in complaining about that in a few real-world aviation magazines some years ago when they made those changes to the JAR rules, changes which included not bothering to teach people how to recover from a spin. I wrote many letters about it, but it was all for nothing. ... to me it is shameful that the authorities would consider it not important for a pilot to know how to do recover from a spin when they know for a fact that it has led to many deaths, and not just in old WW1 biplanes ...

Your message is interesting and alarming in equal measure. Surely this is not just for the professional publications? It is a major, latent, issue of public safety.It seems that the current approach to training assumes that an airliner will not enter a stall without pilot error. If so, it implies a further assumption: namely, that pilots will not make errors leading to a stall. The first assumption is imprudent; the second is absolutely irresponsible.An airline pilot who cannot correct a recoverable mistake merely because his training assumed he wouldn't make it to begin with, should not be asked (or allowed) to fly IMHO. The stakes are too high.Tim

You'll be even more alarmed to hear that Airbus, prior to AF447, considered the Airbus FBW aircraft unstallable, hence no formal training on stalls and recovery.Talk about arrogance!Needless to say that attitude has changed, and new procedures and training methods are already being implemented for all crews of Airbus FBW aircraft.Best regards,Robin.

The above postings keep leading me back to my initial post at the very start of this topic which was: RSR quoted: " the aerodynamic forces of the 800 are nearly perfectly simulated on the NGX." I assume from that being said that the 800NGX will exhibit the actual stall characteristics of the 800 NG, or is there a limitation to this because of FSX programming?Regards,jen noulet

Flight Test with stall of the older 737-400 using auto slats

Very interesting video! It's amazing how stalling is just basic physics...

You'll be even more alarmed to hear that Airbus, prior to AF447, considered the Airbus FBW aircraft unstallable, hence no formal training on stalls and recovery.Talk about arrogance!

I guess they forgot about Titanic... lolAnyway, wasn't there a stall issue on a test flight (something to do with A FLOOR not operating), and a crash video can be found on YT?

Anyway, wasn't there a stall issue on a test flight (something to do with A FLOOR not operating), and a crash video can be found on YT?

I immediately thought the same... 26 June 1988; Air France A320; Flight 296Q; near Mulhouse-Habsheim Airport, France: The aircraft crashed into trees during an air show maneuver when the aircraft failed to gain height during a low pass with the gear extended. Three of the 136 passengers were killed.

You are probably thinking of the A320 crash of AF296 at Habsheim. That was caused by poor piloting decisions more than anything else. The crew flew an airshow flyby down a runway they had not done a briefing for. They were expecting to fly down a different flight line at that air display but were surprised to find that the crowd were aligned along a smaller grass runway. But instead of orbiting and briefing for what they would do upon discovering that the crowd on the airfield were lining a different runway, they simply rolled in made it up as they they went along, which is a very silly thing to do, especially with passengers on board.They did not realise there were trees at the end of that runway and they got below the treeline height, flying along the runway at idle thrust and pulling back on the yoke to demonstrate the stall protection systems, which did work, unfortunately, in that case they worked a bit too well and prevented the aircraft from pulling up over the trees. By the time they got on the throttles (very late) it was too slow to do anything.Al

They did not realise there were trees at the end of that runway and they got below the treeline height, flying along the runway at idle thrust and pulling back on the yoke to demonstrate the stall protection systems, which did work, unfortunately, in that case they worked a bit too well and prevented the aircraft from pulling up over the trees. By the time they got on the throttles (very late) it was too slow to do anything.

...so the official line goes.They never did discover why the last minutes of the FDR went missing or who maybe did it, or why over a week went by before the authorities could get their hands on the boxes.The Captain tried hard to get power as the CVR showed. He keeps referring to "it's not responding", meaning the throttles. This is before they hit the trees...Why is it so hard to believe that the crew are telling the truth and a new control system is malfunctioning? Not the first time bad software has crashed an Airbus. A330 test flying new AP software for a start!Best regards,Robin.

It is known that the power on AF296 was actually applied 5.5 seconds before impact. The N1 speeds half a second before impact were 83 percent on the port engine and 84 percent on the starboard engine, rising to 91 percent for both engines at the time of impact. This was SNECMA's data not EADs by the way, but in any case, that data was cross-referenced with spectral analysis of the sound recordings from the well known video of the crash, as well as the sound on the CVR and the DFDR, and it all tallies up.The crew's belief that the engines were failing to respond is almost certainly because they were at flight idle initially. this is relevant because at 29 percent N1, the CFM 56 engines need four seconds to accelerate up to 63 percent N1, but from 63 percent N1, there is only one second required for the engines to then spool up to 83 percent N1, thus it is not a smooth even curve for engine acceleration, but considerably more laggy when going from flight idle, and when you are looking at a potential crash from the pointy end of an airliner, those four seconds probably slow down in your mind to stretch into an eternity. Pilots of course are normally aware of this spool up lag on gas turbines and why they should be wary of it; that's why on take off they always advance the throttles to 70 percent, and then a bit more once again when powering up. If they instead rammed the thrust levers all the way forward in one go, because the difference in N1 rotation speed from 63 percent N1 is much quicker, should the throttles be unevenly advanced, it would instigate a yaw on the take of roll from asymmetric thrust that would be hard to counter with little or no airflow over the rudder.But even if we don't believe all that evidence about N1 speeds, and even if the tales about the FDRs being switched and doctored are true, we cannot ignore the fact that there is a video which clearly shows that the aircraft was thirty feet off the deck of a runway designed for GA type aircraft, in a dirty configuration, below the height of the trees and pylons ahead of it, on a flight track they had not briefed for, doing a maneuver they had not briefed for, ending up wallowing along at 15 degrees nose up with 122 knots on the ASI as a result of that poor planning and even poorer risk assessment. The flight protection system on the Airbus might be clever, but like Scotty, it cannot change the laws of physics, and any airline pilot you like will tell you that an airliner full of passengers and fuel for the trip it was due to make after the display is not going to like going into a steep obstacle-clearing climb at 122 knots in that configuration, and sadly, we have a video of what happens if you try it.Al

It is known that the power on AF296 was actually applied 5.5 seconds before impact. The N1 speeds ...

That was probably the best and clearest explanation on the Habsheim accident I've ever read. Thanks Al.Tero