# The altitude when Air France 447 could no longer recover **URL:** \ **Category:** Factual Questions\ **Created:** [December 16, 2014, 3:13am UTC](https://boards.straightdope.com/t/the-altitude-when-air-france-447-could-no-longer-recover/707353 "2014-12-16T03:13:34Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [December 17, 2014, 7:35pm UTC](https://boards.straightdope.com/t/the-altitude-when-air-france-447-could-no-longer-recover/707353/21 "2014-12-17T19:35:04Z")
> [@Richard\_Pearse](#): > > 200 mph is ~ approach speed. The jet will very quickly accelerate through that, really quickly. I’d expect it to be on the barbers pole if not faster during the pull, so 330 knots indicated air speed, plus about 50 knots because the higher your altitude the greater the difference between true air speed and indicated air speed. 440 mph would be close to the mark IMO. OK, so instead of going from 50 MPH to 200 MPH, we go to 440 MPH. So average speed during downhill run is 245 mph, while accelerating at 0.75 g’s to final speed. 18 seconds required, during which time they lose 3234 feet of altitude. pulling out of a dive at 440MPH and 3.42 g’s (sticking with the figure I used previously), the turn radius is 3782 feet. But - and I forgot to account for this earlier - if the plane is only in a 30-degree dive, then it doesn’t use up 3782 feet of altitude to achieve level flight; it only needs (1-cos(30))\*3782 = 507 feet. 45-degree dive? OK, 1108 feet. Add in the 1819 feet of altitude they lose while trying to achieve a nose-down attitude, and you get 1819+1108+3234 = 6160 feet of altitude as the bare minimum required for recovery, assuming skilled pilots who know what 3.42 g’s feels like, and assuming the aircraft can generate enough lift at 440 MPH to achieve 3.42 g’s without stalling the wings. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [December 17, 2014, 8:44pm UTC](https://boards.straightdope.com/t/the-altitude-when-air-france-447-could-no-longer-recover/707353/22 "2014-12-17T20:44:00Z")
> [@Machine\_Elf](#): > > The whole thing started with an iced-up pitot tube, but that resolved itself after about a minute, at which point all instrumentation was behaving as designed by the engineers. The problem was that they ended up in a situation with extremely low forward airspeed (and a high AoA) so that the computer decided “this cannot possibly be real,” and so it silenced the stall warning horn. When the pilot pushed forward on the stick, the AoA decreased enough to where the computer decided “OK, _now_ it’s a real stall,” and turned on the stall warning horn. This confused the crap out of the pilots, who then released the stick (at which point the system was only receiving the input from Bonin’s pulled-back stick, so resumed the plane’s high-alpha orientation). Between Bonin’s stick-back shenanigans and the plane’s turn-on-the-stall-horn-when-the-plane pitches-down, they had no idea WTF was going on. Agreed. As far as it goes. The behavior where the stall warning sounded when they were less stalled but stopped when they were more stalled may have been by design. It certainly wasn’t known to the crew. So from their POV it amounted to a malfunction; systems designed and intended to guide their behavior did in fact guide their behavior: in exactly the wrong direction. The real punch line to the whole thing is your statement “… they had no idea WTF was going on.” And they had 3-ish minutes to figure it out. And the symptoms were changing as they descended and as the pitot tubes deiced. Not an easy problem. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [December 17, 2014, 8:58pm UTC](https://boards.straightdope.com/t/the-altitude-when-air-france-447-could-no-longer-recover/707353/23 "2014-12-17T20:58:03Z")
> [@CannyDan](#): > > … He’d say “I want to scream at them GODDAMNIT, just _FLY THE FUCKING AIRPLANE!”_ > > He never mentioned an Airbus edict along those lines. I assumed it was indicative of today’s pilots coming up in the digital age of sims and computer games. But perhaps corporate philosophy reinforced that. … It has a lot more to do with modern airplane design than it does a generation gap. Complex systems fail in complex & subtle ways. In the Olden Dayes airplanes were inherently simple machines with inherently simple failure modes. Systems interaction was minimal. Pilots were taught block-diagram level understandings of how each system was built and operated, and were expected to interpret the signs of malfunction themselves, arrive at a diagnosis, and perform whatever mitigation seemed appropriate. Nowadays that approach is more than deprecated; it’s prohibited and will get your butt chewed by the Feds or your boss if you approach malfunctions that way. So now we’re supposed to run the written fault tree analysis and if there isn’t one, or the situation is ambiguous, we’re totally on our own. Try to keep the shiny side up & land ASAP. That’s not to say basic airmanship and aircraft handling skills are deprecated. They’re just harder than ever to get and keep sharp. For pilots who’ve spent their whole careers on highly automate3d aircraft in highly automated corporate cultures those skills may have never been developed to a high level in the first place. When the first highly automated jets came out and were being flown by guys with a whole career on primitive jets the standing joke was “I’ve forgotten how to fly but can now type 50 wpm” The underlying problem AF447 faced was one of these: [Byzantine fault - Wikipedia](http://en.wikipedia.org/wiki/Byzantine_fault_tolerance) Which is also the problem the Airbus engineers faced. How to interpret and react when some systems are lying to you and you’re not sure which ones they are? Or you’re not even sure whether they’re lying or not? IMO … This accident, and another almost-accident I’ve read about, demonstrate cases where the Airbus engineers designed a system which is simultaneously too smart & too dumb. It’s a brittle failure mode where it’s helping you a bunch until suddenly and with little warning it switches sides and starts trying real hard to kill you. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [December 17, 2014, 9:02pm UTC](https://boards.straightdope.com/t/the-altitude-when-air-france-447-could-no-longer-recover/707353/24 "2014-12-17T21:02:48Z")
> [@Machine\_Elf](#): > > OK, so instead of going from 50 MPH to 200 MPH, we go to 440 MPH. So average speed during downhill run is 245 mph, while accelerating at 0.75 g’s to final speed. 18 seconds required, during which time they lose 3234 feet of altitude. > > pulling out of a dive at 440MPH and 3.42 g’s (sticking with the figure I used previously), the turn radius is 3782 feet. But - and I forgot to account for this earlier - if the plane is only in a 30-degree dive, then it doesn’t use up 3782 feet of altitude to achieve level flight; it only needs (1-cos(30))\*3782 = 507 feet. 45-degree dive? OK, 1108 feet. > > Add in the 1819 feet of altitude they lose while trying to achieve a nose-down attitude, and you get 1819+1108+3234 = 6160 feet of altitude as the bare minimum required for recovery, assuming skilled pilots who know what 3.42 g’s feels like, and assuming the aircraft can generate enough lift at 440 MPH to achieve 3.42 g’s without stalling the wings. I don’t know where you’ve gotten the 3.42Gs from. I’m not asserting you’re wrong, I’m asking the question. The minimal info I have on Airbus flight controls would seem to indicate they’d limit the pilots to 2.5G. Regardless of that quibble, it’s clear that for a sizeable fraction of the plunge from cruise altitude the situation was, as a matter of physics, recoverable. Whether it was recoverable as a matter of man / machine interface and crew dynamics for the given crew on the given day is a separate and much more interesting question. ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [December 17, 2014, 9:17pm UTC](https://boards.straightdope.com/t/the-altitude-when-air-france-447-could-no-longer-recover/707353/25 "2014-12-17T21:17:04Z")
> [@LSLGuy](#): > > I don’t know where you’ve gotten the 3.42Gs from. I’m not asserting you’re wrong, I’m asking the question. The minimal info I have on Airbus flight controls would seem to indicate they’d limit the pilots to 2.5G. It came from md2000’s post (#5). I used it in my first analysis, then just stuck with it. It’s not too different from the “150% of 2.5 Gs” that you described (although FBW won’t let you deliberately exceed that 2.5-G limit). If 2.5 G is the limit, then that means the turn radius increases by ~50%, so add another 500 feet to the altitude requirement. FBW also means skilled aerobatic piloting isn’t required; just pull back on the stick as hard as you can and let the FBW system limit you to 2.5 G. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [December 17, 2014, 9:24pm UTC](https://boards.straightdope.com/t/the-altitude-when-air-france-447-could-no-longer-recover/707353/26 "2014-12-17T21:24:17Z")
> [@AK84](#): > > At 30,000, 20,000 and 15,000 feet how long would you have to recover before you past irrecoverable altitude. They were descending at roughly 10,000 ft. per minute. So if we assume, _arguendo_, that 10,000 ft. was the lowest altitude a perfectly flown maneuver would have cleared the ocean, then they had roughly 2 minutes, 1 minute, and 30 seconds respectively to sort the problem out starting from your three altitudes. If someone wanted to believe recovery from 5000 above the ocean was possible, then add 30 seconds to each estimate. > [@Bullitt](#): > > … Curious, what did you fly in the military? F-16A. > [@Leo\_Bloom](#): > > Flying level, what is the lowest altitude a passenger aircraft is allowed to fly at? There aren’t any special regs about passenger jets vice other aircraft. So 1000’ above the ground or nearby obstacle would be a generally applicable lower limit speaking just to regulations. As a practical matter very short hops might only climb to 2 or 3000 feet. e.g. flying between any of Oakland, San Jose, or San Francisco. Or between Newark, JFK & LGA. Which is also about the altitude we’d use at any airport if making a go-around and needing to reposition for another approach. Sustained longer-duration cruise will normally climb at/above 10,000 above sea level to get above the 250 knot speed limit. We used to fly the 35 miles between PUB & COS at 10,000 or 11,000 feet so we could go 330 knots. Given the terrain there on the front bench is around 6000 feet above sea level we were 4000 - 5000 feet above the ground. Any longer flights the most efficient procedure is to climb until it’s time to descend. For even a 100 mile flight we’ll be apexing at 20-some thousand. So while one could legally fly lower, it Simply Isn’t Done. ---
**Author:** ![Bullitt](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bullitt/32/5725_2.png) [@Bullitt](https://boards.straightdope.com/u/Bullitt)\ **Post date:** [December 18, 2014, 5:43am UTC](https://boards.straightdope.com/t/the-altitude-when-air-france-447-could-no-longer-recover/707353/27 "2014-12-18T05:43:08Z")
> [@LSLGuy](#): > > F-16A. Cool. My brother flew the F-16 when he was a zoomie. Before that he was in the FB-111. Don’t know which flavors of those, though. I’ll ask him when I see him next week at our Christmas family reunion. When he was at Luke in the mid-1990s he got me into the sims and we did a low-lever buzz of the Vegas strip at night. That was a nice light show. Every time he tried to get me to land the F-16, though, I crashed and burned. No matter how much he tried to help me. I was better at artillery FDC, so I should stick to that (USMC). He also worked at Johnson Space Center with the shuttle landing scenarios, and he got us into those sims too. That was fun. He proved that you could barrel roll and then loop the space shuttle before bringing it to a nice smooth landing at Edwards. Anyway back to AF447 - that PM article that Xema linked to upthread was riveting reading. I’ll read it again because the flight situations don’t come too quickly to a ground-pounder like me. I’d like to discuss it with my brother, too. But from my first reading it sounds like the crash is mostly due to pilot error - Bonin, specifically. I’ll re-read it tonight, though. ---
**Author:** ![Bullitt](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bullitt/32/5725_2.png) [@Bullitt](https://boards.straightdope.com/u/Bullitt)\ **Post date:** [December 18, 2014, 6:36am UTC](https://boards.straightdope.com/t/the-altitude-when-air-france-447-could-no-longer-recover/707353/28 "2014-12-18T06:36:12Z")
I realize these are old, but I’m adding links for: BEA Final Report, Jul 2012: [http://www.bea.aero/en/enquetes/flight.af.447/rapport.final.en.php](http://www.bea.aero/en/enquetes/flight.af.447/rapport.final.en.php) CVR complete transcript: [http://www.bea.aero/docspa/2009/f-cp090601.en/pdf/annexe.01.en.pdf](http://www.bea.aero/docspa/2009/f-cp090601.en/pdf/annexe.01.en.pdf) ---
**Author:** ![Velocity](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/velocity/32/18006_2.png) [@Velocity](https://boards.straightdope.com/u/Velocity)\ **Post date:** [December 18, 2014, 4:27pm UTC](https://boards.straightdope.com/t/the-altitude-when-air-france-447-could-no-longer-recover/707353/29 "2014-12-18T16:27:40Z")
> [@Xema](#): > > Because they had substantial engine thrust, the plane’s descent wasn’t close to vertical - it was actually around 40 degrees from horizontal. > > And only a small relaxation in the stick-held-fully-aft problem would have led to controlled flight. This actually happened around 2 minutes into the problem, when the junior pilot let his stick go forward a bit, and airspeed increased from 93 to 223 kts. But he then pulled the stick fully aft again, where it stayed for the rest of the flight. > > This near-recovery to me suggests that had the pilots become aware of what was happening and put the stick forward, recovery would have been possible even from a fairly low altitude. The airspeed increase mentioned above (which was due only to a relaxation in back-stick position, not a vigorous forward movement) took just 21 seconds. The plane was descending at around 10,000 fpm, which argues that 3500’ would have been sufficient (perhaps less, given that the rate of descent would have slowed during a recovery maneuver). If this is true, it seems like AF447 is a testament to how \*well \*the A330 performs in a stall. ---
**Author:** ![Velocity](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/velocity/32/18006_2.png) [@Velocity](https://boards.straightdope.com/u/Velocity)\ **Post date:** [April 22, 2015, 8:19pm UTC](https://boards.straightdope.com/t/the-altitude-when-air-france-447-could-no-longer-recover/707353/30 "2015-04-22T20:19:56Z")
Has the control-stick feedback problem been fixed? (Where one pilot could not tell that the other pilot was pulling back on the stick). ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [April 22, 2015, 8:31pm UTC](https://boards.straightdope.com/t/the-altitude-when-air-france-447-could-no-longer-recover/707353/31 "2015-04-22T20:31:13Z")
> [@Velocity](#): > > Has the control-stick feedback problem been fixed? (Where one pilot could not tell that the other pilot was pulling back on the stick). This article indicates that the pilot and co-pilot now receive an audible warning. [http://news.aviation-safety.net/2015/03/23/report-wedged-camera-at-sidestick-causes-airbus-a330-loss-of-altitude-incident-2/](http://news.aviation-safety.net/2015/03/23/report-wedged-camera-at-sidestick-causes-airbus-a330-loss-of-altitude-incident-2/) > [@](#): > > Both pilots report hearing a dual input audio warning, indicating simultaneous inputs by both pilots on their respective side-sticks. In the incident described in that article, the captain had accidentally wedged a camera in between his seat and the control stick and unintentionally commanded the plane into a dive when he adjusted his seat. When the co-pilot pulled back on his stick to correct for the dive, they got the warning. ---
**Author:** ![Velocity](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/velocity/32/18006_2.png) [@Velocity](https://boards.straightdope.com/u/Velocity)\ **Post date:** [April 22, 2015, 8:33pm UTC](https://boards.straightdope.com/t/the-altitude-when-air-france-447-could-no-longer-recover/707353/32 "2015-04-22T20:33:46Z")
Thanks, good info. ---
**Author:** ![Bear\_Nenno](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bear_nenno/32/3358_2.png) [@Bear\_Nenno](https://boards.straightdope.com/u/Bear_Nenno)\ **Post date:** [April 22, 2015, 8:57pm UTC](https://boards.straightdope.com/t/the-altitude-when-air-france-447-could-no-longer-recover/707353/33 "2015-04-22T20:57:28Z")
> [@Velocity](#): > > Has the control-stick feedback problem been fixed? (Where one pilot could not tell that the other pilot was pulling back on the stick). No. They just retrained and reminded all the pilots of this “feature”. There are two philosophies with respect to Fly-by-wire designs. Airbus prefers the simplicity of their system, and they’re sticking with it. Boeing has a design that more closley mimics traditional, mechanical controls. ---
**Author:** ![Bear\_Nenno](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bear_nenno/32/3358_2.png) [@Bear\_Nenno](https://boards.straightdope.com/u/Bear_Nenno)\ **Post date:** [April 22, 2015, 9:03pm UTC](https://boards.straightdope.com/t/the-altitude-when-air-france-447-could-no-longer-recover/707353/34 "2015-04-22T21:03:21Z")
> [@Bear\_Nenno](#): > > … and they’re sticking with it. No pun intended. ---
**Author:** ![Kent\_Clark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kent_clark/32/105_2.png) [@Kent\_Clark](https://boards.straightdope.com/u/Kent_Clark)\ **Post date:** [April 22, 2015, 9:35pm UTC](https://boards.straightdope.com/t/the-altitude-when-air-france-447-could-no-longer-recover/707353/35 "2015-04-22T21:35:32Z")
> [@LSLGuy](#): > > The no-kidding limit case answer depends on a lot of unknown factors. Such as what was their forward & vertical speed, were the engines still running, are we assuming the instruments suddenly started working and the pilots became unconfused Chuck Yeagers, or would this be a tentative effort by confused scared folks in the dark guessing at their true aircraft state? Speaking of Yeager, in a section of [this interview](http://www.achievement.org/autodoc/page/yea0int-2) he talks about two of his more famous stalls. He stalled the X1-A at 80,000 feet and needed 51 seconds to recover, during which time the X1-A fell to 25,000 feet. The second stall was with the F-104, as seen in _The Right Stuff._ It stalled at 104,000 and Yeager was never able to get the nose down. He ejected at 6,000 feet. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [April 22, 2015, 11:48pm UTC](https://boards.straightdope.com/t/the-altitude-when-air-france-447-could-no-longer-recover/707353/36 "2015-04-22T23:48:30Z")
> [@Velocity](#): > > Has the control-stick feedback problem been fixed? (Where one pilot could not tell that the other pilot was pulling back on the stick). It’s been fixed in the sense that they realize it’s a potential problem and most aircraft delivered in the last couple years have the revised software which sounds the alert as pointed out by **engineer\_comp\_geek**. The fix has not been retrofitted to all Airbus aircraft everywhere, nor is it (yet) required to be, at least not by FAA. ---
**Author:** ![Musicat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/musicat/32/20189_2.png) [@Musicat](https://boards.straightdope.com/u/Musicat)\ **Post date:** [April 23, 2015, 12:15am UTC](https://boards.straightdope.com/t/the-altitude-when-air-france-447-could-no-longer-recover/707353/37 "2015-04-23T00:15:14Z")
> [@Xema](#): > > It’s a sobering thought that if the three pilots had decided to get up and walk off the flight deck, the plane would have been fine. I understand what you are saying, but is this really true? If the pilots had removed their hands from the controls not long after all the warnings, would the plane have had enough time and height to keep flying, even if they had to skim the waves? And isn’t this the essence of this thread? ---
**Author:** ![Richard\_Pearse](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/richard_pearse/32/13144_2.png) [@Richard\_Pearse](https://boards.straightdope.com/u/Richard_Pearse)\ **Post date:** [April 23, 2015, 12:48am UTC](https://boards.straightdope.com/t/the-altitude-when-air-france-447-could-no-longer-recover/707353/38 "2015-04-23T00:48:19Z")
> [@Velocity](#): > > Has the control-stick feedback problem been fixed? (Where one pilot could not tell that the other pilot was pulling back on the stick). I’ve just had a browse through the final report and this issue isn’t really addressed at all. It is not listed as a causal factor or discussed in the text of the report. Also as I understand it the issue wasn’t so much of dual inputs being received, the FO was applying the sole input for most of the time, but more that the fact of the FO’s nose up input was not available to the other crew. The audio warning “DUAL INPUT” doesn’t solve this. ---
**Author:** ![Bear\_Nenno](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bear_nenno/32/3358_2.png) [@Bear\_Nenno](https://boards.straightdope.com/u/Bear_Nenno)\ **Post date:** [April 23, 2015, 12:57am UTC](https://boards.straightdope.com/t/the-altitude-when-air-france-447-could-no-longer-recover/707353/39 "2015-04-23T00:57:16Z")
> [@Music Cat](#): > > I understand what you are saying, but is this really true? If the pilots had removed their hands from the controls not long after all the warnings, would the plane have had enough time and height to keep flying, even if they had to skim the waves? And isn’t this the essence of this thread? The first alarm they received was simply an idicator that the plane came off auto pilot. Had Bonin touched nothing at this point, everything would have probably been fine. “So here is the picture at that moment: the airplane was in steady-state cruise, pointing straight ahead without pitching up or down, and with the power set perfectly to deliver a tranquil .80 Mach. The turbulence was so light that one could have walked the aisles—though perhaps a bit unsteadily. Aside from a minor blip in altitude indication, the only significant failure was the indication of airspeed—but the airspeed itself was unaffected. No crisis existed. The episode should have been a non-event, and one that would not last long. The airplane was in the control of the pilots, and if they had done nothing, they would have done all they needed to do.” From here: [Should Airplanes Be Flying Themselves? | Vanity Fair](http://www.vanityfair.com/news/business/2014/10/air-france-flight-447-crash) ---
**Author:** ![JKellyMap](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jkellymap/32/15880_2.png) [@JKellyMap](https://boards.straightdope.com/u/JKellyMap)\ **Post date:** [April 23, 2015, 10:58am UTC](https://boards.straightdope.com/t/the-altitude-when-air-france-447-could-no-longer-recover/707353/40 "2015-04-23T10:58:58Z")
Okay, but the question at hand now is, “what is the latest point in the event at which simply letting go of all controls would have saved them?” [Previous page](https://boards.straightdope.com/t/the-altitude-when-air-france-447-could-no-longer-recover/707353.md?page=1) [Next page](https://boards.straightdope.com/t/the-altitude-when-air-france-447-could-no-longer-recover/707353.md?page=3)