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Well, another air tragedy and another learning chance. That is what science is all about. You learn from your failures and disasters. Scientists take these things in their stride.

So what caused AirAsia Flight QZ8501's crash? What lessons can we learn?

According to initial information AirAsia Flight QZ8501 made an "unbelievably" steep climb before it crashed, possibly pushing it beyond the Airbus A320's limits. The data was transmitted before the aircraft disappeared from the screens of air traffic controllers in Jakarta on that fateful day of 28th Dec., 2014. These findings sharpen the focus on the role bad weather and the crew's reaction to storms and clouds in the area had to play in the plane's crash into the Java Sea which killed all 162 people on board. Although cockpit voice recorder and flight data recorder haven't been found yet, for a full picture to come into our focus, the information we got till now point to certain blunders the pilots made.

This is the picture we get now...

At 6.12 a.m. on that day, 36 minutes after taking off from Surabaya's Juanda Airport on a flight to Singapore, the pilot asked for permission to climb to 38,000ft from 32,000ft and deviate to the left to avoid bad weather caused by a storm.

Two minutes later, Jakarta responded by asking QZ8501 to go left seven miles and climb to 34,000ft. There was no response from the cockpit. The aircraft was still detected by the ATC's radar before disappearing at 6.18 a.m.

An image that was reportedly leaked from AirNav Indonesia, which manages the country's air space, and shared on several websites, appeared to show QZ8501 at an altitude of 36,300ft and climbing at a speed of 353 knots.

If this is accurate, the image and information released so far pointed to the fact that the aircraft may have climbed suddenly and then lost speed. This can result in the aircraft stalling in mid-air before plunging to the sea.

Now what is stalling? Stalling in lay man's words is equal to the 'engine quitting'. To a non-pilot, a stall can best be described as the situation where there is not enough air flowing over the wings to create the amount of lift needed to hold up the airplane. Pilots will be trained to cope with these and learn the telltale signs that occur just before it happens and to make the recovery procedure automatic. If pilots can recognize an impending stall, they can take corrective action to either avoid the stall altogether or to recover as quickly as possible from such situations (1, 2).

Stalls typically only occur shortly before landing and after takeoff, when the pilot gets distracted while already at a slow speed. In both of these situations the airplane is very close to the ground, immediately requiring the correct action from the pilot in order to avoid a crash. This needs to be instinctive and corrected using muscle memory so that it is accomplished as rapidly as possible.

You can also stall from over speed (exceeding the critical mach number) and from flying too high.

Sufficient airspeed must be maintained in flight to produce enough lift to support the airplane without requiring too large an angle of attack. At a specific angle of attack, called the critical angle of attack, air going over a wing will separate from the wing or "burble" , causing the wing to lose its lift (stall). The airspeed at which the wing will not support the airplane without exceeding this critical angle of attack is called the stalling speed. This speed will vary with changes in wing configuration (flap position). Excessive load factors caused by sudden manoeuvres, steep banks, and wind gusts can also cause the aircraft to exceed the critical angle of attack and thus stall at any airspeed and any altitude. Speeds permitting smooth flow of air over the airfoil and control surfaces must be maintained to control the airplane (2).

Stalls are of three types:

Departure Stalls (can be classified as power-on stalls) are practised to simulate takeoff and climb-out conditions and configuration. Many stall/spin accidents have occurred during these phases of flight, particularly during overshoots. A causal factor in such accidents has been the pilot’s failure to maintain positive pitch control due to a nose-high trim setting or premature flap retraction. Failure to maintain positive control during short field takeoffs has also contributed towards accidents.

Arrival Stalls (can be classified as power-off stalls or reduced power stalls) are practised to simulate normal approach-to-landing conditions and configuration. Simulations should also be practised at reduced power settings consistent with the approach requirements of the particular training aircraft. Many stall/spin accidents have occurred in situations, such as crossed control turns from base leg to final approach (resulting in a skidding or slipping turn); attempting to recover from a high sink rate on final approach by using only an increased pitch attitude; and improper airspeed control on final approach or in other segments of the traffic pattern.

Accelerated Stalls can occur at higher-than-normal airspeeds due to abrupt and/or excessive control applications. These stalls may occur in steep turns, pull-ups, or other abrupt changes in flight path. For these reasons, accelerated stalls usually are more severe than un-accelerated stalls and are often unexpected.
The third situation might be responsible for this aircraft to crash into the sea.
An A320 would cruise at a speed of around Mach 0.78 while at an altitude of 32,000ft. That translates into roughly 516 knots.

If you encounter turbulence, you go slower at what the pilots call the turbulence penetration speed to get through it. If you climb to avoid turbulence, you slow down to have a better climb rate. That could be around Mach 0.76. But if you climb suddenly and start to lose speed, you will stall.

There could be parallels between this incident and the crash of Air France flight AF447 in 2009. The investigation into that Airbus A330 showed that the co-pilot lost speed readings due to icing on the airframe. His panic reaction meant that he kept trying to climb despite repeated stall warnings, and the crew failed to recognize the situation, eventually sending the aircraft plunging into the Atlantic.

Fortunately, airplanes are designed so that even during a stall the tail is still effective and the pilot is able to use it to force the nose down. This makes the airplane go faster, since it is pointed down towards the ground, and gets more air moving over the wing which allows it to create enough lift for the airplane to start flying again. During practice it is usually pretty uneventful, but when it happens in real situations there may not be enough time to regain flying speed before the airplane crashes. The A320's systems usually prevent pilots from doing anything outside usual safe flight parameters. But these protections can be disabled in some circumstances, handing control to the pilots and leaving it to manual flying skills. And pilots are human beings, despite all the training they get, they can still panic and might sometimes take extreme measures or fail to correct the situation in time resulting in disasters. And the weather and turbulent storms make things worst for them too.

Despite all the science we know that can cause these tragedies, the human element involved makes us realize we are still very weak before natural forces and cannot utilize our knowledge under some circumstances. Instructors should concentrate on these things while giving training to people who fly these machines.

References:

1. http://aviation.stackexchange.com/questions/1418/what-happens-when-...

2. http://www.pilotfriend.com/training/flight_training/fxd_wing/stalls...

Views: 562

Replies to This Discussion

http://www.aerofiles.com/glossary.html

558

why doesn't the tail hit the runway when a plane  lifts off...

https://www.quora.com/When-the-plane-takes-off-why-doesnt-the-tail-...

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According to data collected by the Aviation Safety Reporting System (FAA), the commercial aviation industry experiences nonfatal incidents on a regular basis.

These self-reported incidents include critical altitude deviation, fuel management issues, smoke and fire in the cabin, in-flight weather encounters, mechanical issues due to unreliable maintenance, crew fatigue, medical fitness of pilots, near midair collisions with another plane and near midair collisions with unmanned aerial vehicles, or drones. Despite the fact that all these incidents reported to the ASRS were not associated with any direct loss of life, many of them pose severe risk to passenger security.

For instance, FAA statistics suggest that there were more than 700 near midair collisions between airplanes and drones in 2015.

For the same year, FAA has reported 28 critical near midair collisions

http://www.scientificamerican.com/article/is-commercial-aviation-as...

Air France 447 Probe Raises Questions about Stall Warning Ergonomics
http://www.ainonline.com/aviation-news/air-transport/2012-07-23/air...
Can Airlines Protect Passengers from Malfunctions and Misuse?
An air safety expert talks about automated cockpits and when, if ever, commercial aircraft will be piloted remotely
http://www.scientificamerican.com/article/can-airlines-protect-pass...

You trust the automation. When it’s working okay, everything is fine. When something fails, a lot of times the failure itself may be something subtle and the crew starts focusing on what the problem is and forgets to fly the airplane. That’s been true in several accidents. Aviation psychology folks call that “automation complacency,” and it makes us slow to react to certain situations.

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https://www.quora.com/What-was-the-most-incredibly-stupid-and-avoid...

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