44
It isn't practical for a number of reasons:
Intentional stalls are inherently dangerous. Stall-spin accidents are a major cause of accidents, stall recognition and recovery are taught specifically to avoid stalls. Some airplanes have docile stall characteristics, but even those can still bite you. A Cessna 172 will drop a wing if mishandled, especially ...
36
You only feel the acceleration downward. In roller-coaster this sensation is maximized for maximum thrill. A stall isn't instant: some parts of the wing can be stalled while the rest still provides proper lift. Once the airplane is near or at terminal velocity in a stall it will feel no different from regular straight and level flight.
The onset of the ...
32
Stalls occur based on a wing's angle of attack rather than the aircraft's airspeed. (In fact, one of the basic facts that all pilots learn in their initial training is that an airplane can stall at any airspeed). The A330 measures angle of attack using vanes mounted on the fuselage:
However, below 60 knots, these vanes become ineffective. During the ...
31
For the stalled flight to recover, the nose needs to be pointed in the airstream, and then the aircraft pulled up with load factor below the ultimate load. From the accident report:
The recordings stopped at 2 h 14 min 28. The last recorded values were a vertical speed of -10,912 ft/min, a ground speed of 107 kt, pitch attitude of 16.2 degrees nose-up
...
29
You only feel the plunging sensation during the initial downward acceleration. Once stabilized at a constant rate of descent, things feel normal again. The other thing is, the amount of vertical acceleration from a stall type maneuver does not result in 0 or negative G, just less than 1. You'll feel getting light in the seat, you won't lift right out and ...
22
Captain Bill Palmer, in his book "Understanding Air France 447" has a section dedicated to answering that very question as it pertains to AF447. Although there is no way to know for certain he puts forward some possibilities.
He quotes a commenter on a website:
One commenter on the Weather Graphics website’s AF447 article provided this interesting ...
21
You don’t need a new technique
You don’t normally stall jetliners. And in a crisis the last thing you want to do is learn a new technique.
Besides, they already have a trained practice for descending jetliners very quickly. It’s used for loss of cabin pressure. While the procedure normally levels at 10,000’/3000m, it could certainly be extended.
Anyway, ...
19
Unfortunately, if there had been a jazz band in the cockpit singing "The plane is stalling" it wouldn't have helped. If Moses had been in there carrying a stone tablet newly-carved by God himself inscribed "Pitch down" with a host of angels to help announce it, that would have made no difference.
The unrecoverable problems were in the pilots' brains and in ...
19
Normally, a stall and controlled flight are mutually exclusive.
That AF447 would descend as it did has to do with the relaxed static stability of the A330 and its rear cg location as well as the docile behavior of its airfoils with large separation on the upper side. In short: With some aircraft this is indeed possible and practical but with others it is ...
17
GPS speed is already available to the crew, although not in an easy to see place. It isn't designed to cross-check other instruments because it is showing entirely different information. The winds are changing the actual speed of the airplane across the ground (which GPS shows) and altitude affects the air density (which changes the airspeed shown on the ...
17
The main issue is that we can only get groundspeed from GPS data. Winds aloft aren't known exactly at a particular place, so they could be rather inaccurate -- certainly not enough to leave to the hands of the autopilot. The decision to use GPS data to verify airspeed would lie in the hands of the crew. Anyway, they were too preoccupied to go and check that ...
16
@mike rodent I've read your comments on this post and they seem rather strong in tone to me. I'm joining the discussion here to hopefully explain to you why your ideas are not going to work as you intended in real life.
The reason for the gap between your proposed solution and other's comment on "it will not work" is that you have a flawed understanding of ...
14
It is smarter to roll onto your side and maintain unstalled flight, executing a emergency spiral descent. G loads on the wings are much lower as there is no need to maintain altitude, only to control airspeed.
With all due respect to our beloved Langewiesche, "mushing glide" technique is for much lower wing loaded gliders that are easily unstalled ...
13
If the system detects anomalies for more than about ten seconds, alternate law becomes locked in for the remainder of the flight.
The system detected a change in the median value of the three airspeed sources of more than 30 knots within one second (it actually dropped from 274 to 52 knots within 3 seconds). That started a process where the system monitors ...
12
A flag is not really effective because a big jets stalling speed is well over 100+ knots. The flag will be blowing fully even in the stall. I'm not familiar with the ship suggestion but it sounds like you're desribing a gyroscope - aka an attitude indicator, which is already right in front of the pilots.
But furthermore, it doesn't solve the problem. AF447 ...
12
What other circumstances may cause the autopilot to trip out?
There are numerous circumstances, a few at random
pilot presses the autopilot disconnect pushbutton.
applying force to control-stick that contradicts autopilot.
entering a stall.
activation of high AoA protection.
descending below MDA on a non-ILS approach.
inconsistent data.
will it not ...
11
Wouldn't these two measures have had a good chance of providing the pilots of AF 447 with a true and totally irrefutable mental picture of what was actually going on?
No more so than the standard indicators of attitude and airspeed that we've had for as long as people have been climbing into flying machines.
Attitude indicator
(source: pilotfriend.com)
...
11
It appears in both situations that the PF had trouble stabilizing the aircraft roll attitude.
Note that roll control is secondary when recovering from a stall.
Restoring normal pitch and roll, he stresses, are "of secondary importance"
The situation required that the pilots heed the stall warnings, be aware of the stall and put the nose down to trade ...
10
I just finished reading this article and couldn't understand why in 3
minutes and 30 seconds even though there was no reliable speed data,
pilot could not level the plane?
If you look at this video by the French accident investigation bureau (BEA) you can see what happened.
The problem started when the speed indicators failed temporarily because of ...
10
You are forgetting one large difference between an aircraft moving through the air (still generating some lift), and an object in free-fall. Constant velocity in a gravity well (such as on the Earth) will cause you to still experience the acceleration due to gravity. It's when you're accelerating that you feel different.
Think of it this way - imagine ...
9
What improvements did Airbus make as a result of the Air France 447 accident?
The official report has a section headed
5 - CHANGES MADE FOLLOWING THE ACCIDENT
...
5.2 Airbus
Review of the “Unreliable speed indication” procedure
Flight Operations Telex (FOT) of 9 September 2009 recommending, at the next recurrent
training course, a session on the simulator ...
9
I‘ll attempt a very brief answer based on the report against your questions:
1) Why did the aircraft stall?
The aircraft stalled because crew pitched the aircraft up beyond the performance limit at that altitude (they pitched into a climb which the available engine thrust could not sustain, bleeding off speed until the aircraft stalled).
2) Why was power ...
8
I'd say this is quite common on flights that require at least 3 pilots due to length. The third pilot is almost assuredly going to be qualified as a first officer and this is the common staffing strategy with the US carriers that I am familiar with.
Three pilots (by US flag rules) are going to be required for 8-12 hour flights and you'll find that US ...
7
I think there is some information lost in translation.
The speeds of 13000 kmph are associated with reentry vehicles. The aircraft won't have had time to accelerate to that speeds in the first place, even if there is no atmosphere.
The (forward) speed is usually measured in mph in US (to the best of my knowledge). The vertical speed is given usually in ...
7
Air France 477 was in a fully developed stall. In a normal flight attitude. All the way from 40,000 feet to the surface of the ocean. The aircraft was falling like a leaf from a tree, with an angle of attack of 90 degrees. No buffeting. Yes they rolled back and forth, again like a leaf in the wind.
Before AF 477, stall training focused on recognising the ...
6
It's not accident speculation when it has been investigated.
The full accident report is available online with a very adequate summary on Wikipedia.
There are many reasons, but from the human factors study:
The final BEA report points to the Human Computer Interface (HCI) of the Airbus as a possible factor contributing to the crash. It provides an ...
6
In AF447 the falling motion most definitely affected the angle of attack. Due to the fact that the pf did keep the stick pulled back for all but the last few seconds of the fall the aircraft was so steep that, although the aircraft was falling at a slight pitch up, angles of attack actually reached as high as 60°.
The descent was so steep that the air was ...
6
While it's certainly possible to come up with scenarios, either historical or suggested by imagination, where passengers would or could know that "something isn't right," the number of scenarios where "false positive" conclusions (taking as an emergency something that in fact, isn't) and "false negatives" (not knowing about something emergent actually going ...
6
One of the survivors (a passenger) of Air Florida Flight 90 was a Private Pilot and
...Stiley, a pilot himself, said he realized that something was wrong as the plane headed down the runway. He said there was still snow and slush on the wings and he remembered wishing he could get off the plane.
source
6
Sensation of motion can come through three of the physical senses. Each of the three senses is successively unavailable as we move through the examples of an amusement park ride, the plummeting elevator, and AF447.
Vision
This sense is fairly well understood, so I'll limit this bullet point to pointing out that the visual sense is correlated in the human ...
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