AirAsia Indonesia Airbus A320 PK-AXF.
AirAsia Indonesia Airbus A320 PK-AXF. Image copyright Devesh Agarwal.

What caused the AirAsia QZ8501 crash? Facts and myths

As the remains of the persons on board the ill fated Indonesia AirAsia flight QZ8501 tragedy are slowly recovered, it is sometimes distressing to hear the answers to the questions from the general populace on why did this tragedy occur.

So we put together a small list of answers to frequently asked questions. We have tried to make it as simple as possible, but there is still quite a bit of jargon involved and if we try to explain it all, we will be writing a novel; and Bangalore Aviation is a site for the aviation enthusiast.

What caused the crash

Very simply we do not know. One hears speculation ranging from the very plausible to the outright ridiculous. The authorities believe the aircraft was a victim of having flown in to an extremely strong thunderstorm so common at this time of year in the inter-tropical convergence zone (ITCZ).

While it is in our human nature to be curious, are we just trying to feed ourselves with some macabre, vicarious thrills? Instead, may we suggest let us focus on some of the facts.

Chronology of the crash

The acting Director General of Civil Aviation of Indonesia, Djoko Murjatmodjo, has delivered the chronology of the loss. All times indicated are WIB which is UTC+7 or IST+1.5.

  • At 05:36 (22:36UTC 27-Dec-14) the plane departed Surabaya to Singapore. It was assigned to fly an altitude of 32,000 feet (Flight level – FL320) and track on the M-635 airway.
  • At 06:12 The aircraft contacted ATC Jakarta on frequency 125.7 MHz and reported FL320. ATC identified the aircraft on radar. The pilot communicating requested to deviate left of M-635 to avoid the cloud [could be the thunderstorm] and to climb to FL380 (38,000ft). [Clues as to why the crew asked for the increase in altitude are explained later in the article]. [There were initial reports that ATC refused the climb request, but it was later clarified that Jakarta ATC coordinated with Singapore ATC and gave approval after a few minutes but there was no response from the plane]
  • At 06:16 the aircraft was seemingly on the radar screen
  • At 06:17 the aircraft was only visible on the ADS-B (automatic dependent surveillance – broadcast) signal. Contact with ATC was lost.
  • At 06:18 the aircraft target disappeared from the radar screen.
  • At 07:08 Jakarta ATC invoked INCERFA (Uncertainty phase of oceanic emergency procedures. Concern about the safety of an aircraft). Basarnas (Badan SAR Nasional – Indonesian Search And Rescue) was informed.
  • At 07:28 ATC escalated to ALERFA (Alert phase. Apprehension on the safety of an aircraft).
  • At 07:55 ATC declared DETRESPA (Distress phase. When there is reasonable certainty that the aircraft and its occupants are threatened by grave and imminent danger) and a missing plane statement was issued. To read more about Oceanic emergency procedures please visit this page of the United States Federal Aviation Administration (FAA)

Fact – AirAsia safety record

AirAsia has an excellent safety record. Other than a few minor incidents, the airline and all its affiliate franchisees, in Indonesia, in India, in Thailand, in The Philippines, in Japan, the airline has not had any major incident, let alone an accident. Recent news that the airline was not flying on a day licensed is an administrative issue since Indonesia AirAsia is licensed to fly between Surabaya and Singapore four times a week and Sundays were not included.

Fact – The Airbus A320 aircraft

The Airbus A320 has a strong safety record. It is one of the best selling aircraft in the world and includes shorter to longer variants called A318, A319, A321 and Airbus Corporate Jet (ACJ). From its first delivery in March 1988, almost 27 years ago, Airbus has delivered almost 6,300 A320 family aircraft, and over 6,000 still fly today. It is estimated that an A320 family aircraft takes off or lands every 2.5 seconds somewhere in the world. In India the erstwhile Indian Airlines now merged into Air India, GoAir, IndiGo, and Vistara operate the A320. Before the AirAsia crash the A320 family had suffered 24 hull-loss accidents with 789 fatalities. This translates to one fatal crash for every 71.43 lakh departures. By comparison all of India had only 1.68 lakh departures last year.

What is this ITCZ?

The inter-tropical convergence zone circles the globe near the equator. Here winds from the northern and southern hemispheres both heading towards the equator collide. The strong sun warms the water which in turn heats and humidifies the air. Warm air rises. The colliding winds are forced upwards by where they cool and become powerful thunderstorms as they release their moisture. Some of these storms top out in the troposphere, about 60,000 feet. The moisture is super-cooled which causes icing on aircraft control and sensor surfaces, and precipitation in the form of hail which can cause engine damage and surges.

Myth – Lighting can damage an aircraft

Again NO. Modern airliners are designed to withstand a lightning strike. The electrical energy is routed along the outer skin of the aircraft and exits from various extension points built into the wing and tail of the aircraft. This video from the Smithsonian shows about lighting and aircraft.

This recording of the ATC at New York’s JFK airport communicating with a JetBlue A320 when it suffers a lightning strike on approach to land. Hear how calmly the pilots and air traffic controllers treat this incident as a matter of routine.

Myth – a storm can tear apart an aircraft

A very emphatic NO. Modern aircraft, with the benefit of modern materials, are designed to be extremely strong …… by being flexible. Just like a reed which bends in the wind but does not break, the wing of a modern jetliner can flex more than 30 feet, and that is the height of three building floor. Airliners can withstand tremendous loads and stresses which are many many times higher than normal flying. As part of its certification, every aircraft model must undergo a ‘flutter test’ in which the aircraft is dived down till it almost achieves the speed of sound, which causes the wings to flutter (hence the name). Then the control column is pulled back and the plane is recovered from the dive, producing incredible stress on the airframe.

Yet, storms are unpredictable and often contain violently strong winds which come at the aircraft from a variety of directions, front, back, up, down, sideways, or a combination. While these winds may not physically damage an aircraft, they can cause an ‘upset’ in the aerodynamic balance of an aircraft. To avoid this pilots routinely ask to “deviate left or right of track” i.e. to go around a storm.

Flying through storms, and the altitude increase – the hype, the facts

Much of mainstream media has tried to create an issue about the pilot requesting an altitude increase just prior to the disappearance from radar.

No pilot willingly or knowingly puts his/her plane and its occupants in danger. Storms are routine of the area and this an accepted fact of flying. The image below shows the vicinity of QZ8501, Many flights of differing airlines are flying. Indonesia’s national carrier Garuda (GIA), Lion Air Indonesia (LNI), Indonesia AirAsia (AWQ), and Emirates airline (UAE). Flight EK409 from Melbourne, Australia to Kuala Lumpur, Malaysia is about 50nm (nautical miles or 55 statute miles or 88 kilometres) ahead of QZ8501 at FL360 at a ground speed of 506 knots. Another Indonesia AirAsia flight, QZ550, is at FL340 at 477 knots, about 50 nm of EK409.

Flightradar24 plot of the vicinity of QZ8501
Flightradar24 plot of the vicinity of QZ8501

Almost all the flights in the vicinity are at an altitude greater than QZ8051. Pilots try to give their passengers the smoothest ride they can and frequently rely on ‘ride-reports’ from aircraft nearby. It is possible the pilots requested the altitude increase looking at the nearby flights.

The views voiced that the pilots were trying to climb over the storm does not hold merit. An A320 can fly maximum around 41,000ft altitude. The extreme storm in front of QZ8501 topped out above 60,000 feet. Pilots are familiar with their local weather, and Captain Iriyanto a seasoned aviator would minimise risk by flying around storms, not through them.

As an aircraft climbs higher, the air becomes thinner, and this reduces the efficiency of the control surfaces and engines. The margins between the maximum speed and the stall speed narrows to a point where is it difficult to fly an aircraft manually. In normal cruise the efficiency of the lower drag of high altitude thin air outweighs the reduction in control, and the autopilot is able to perform this routine task very easily.

Plausible cause of the crash

In the FlightRadar image we have super-imposed an image purported to be a radar screen picture from Indonesia’s ATC AirNav (we cannot vouch for the veracity of the image). If accurate, it shows QZ8501, which was supposed to be at FL320, at FL363 (36,300ft) and climbing. At the same time, the airspeed which would have been around 460~470 knots (based on the other AWQ flights in the vicinity and on a similar track), has dropped to 353 knots, indicating steep ascent. Does this image show flight QZ8051 being pushed violently upwards by the storm winds? Was this the beginning of an aerodynamic upset? This theory is the most plausible in the eyes of the Indonesian authorities as of now. The two black boxes will provide the definitive answers.

The autopilot

The autopilot and system automation have kept pace with the increase in technological progress. On most flights today, the auto-pilot is switched on between two and four minutes after take-off, and switched off about two to four minutes before landing. This automation allows the pilots more time to monitor the progress of the flight, and as in the case of QA8501, identify bad weather and navigate around it. However, as a safeguard, airplane manufacturers disable the autopilot when the flying conditions become extremely abnormal. An example is the case of Air France AF447 which crashed in the Atlantic Ocean in an ITCZ storm on June 1, 2009. In that crash the pitot tubes which measure airspeed and relay their readings to the flight computers, froze. Not receiving accurate air-speed readings the computers switched off the auto-pilot and expected the crew to fly the plane.

An experienced Air India A320 captain explained that similarly, the autopilot on an A320 can disconnect when the aircraft makes very sudden climbs or descents. Was flight QZ8051 suddenly forced upwards by a powerful wind? Did this result in the aircraft slowing down to dangerously low speeds and going in to a stall? Did the auto-pilot disconnect leaving the pilots to manually fly the aircraft at high altitude in extreme winds, a very challenging task even with the electronic aids the Airbus flight computers are famous for?

It is a very real possibility. But again let us not speculate.

No communication? no life-vests?

Much has been made about the lack of a mayday or any emergency communication from the aircraft. A pilot’s job is to first aviate, then navigate, and then communicate. If the flight crew had their hands full with an aircraft aerodynamically upset and in extreme turbulence, they would too busy performing their first duty, i.e. to fly the plane. In the case of Air France AF447, the pilots attempted to fly the plane for more than four minutes before crashing, and never once communicated with ATC. They were too busy trying to understand the situation and recover from it.

Similarly, there is concern voiced about the lack of passengers wearing their life-vests. Again in the case of Air France AF447 most passengers were completely unaware their plane was hurtling towards the Atlantic Ocean till they actually impacted the water. The remains of most souls on board AF447 were found strapped in their seats. This scenario is slowly coming true in the case of the doomed Indonesia AirAsia flight.


Post the disappearance of Malaysia Airlines flight MH370, there is a lot of debate on tracking flights. It is a trade-off between cost and need. There are almost four million flights annually. Tracking each flight will generate huge volumes of data. Who will pay for it? It is really required? Today, with the exception of long distance polar or trans-oceanic flights, most flights are tracked by some form of technology. Be it radar, ADS-B, ADS-C, or ACARS (aircraft communication addressing and reporting system), or even in-flight Wi-Fi which is satellite based and has the side benefit of broadcasting the aircraft’s position. The airline industry body IATA and the United Nations body ICAO (international civil aviation organisation pronounced eye-kay-oh) have declared the need for tracking and have task-forces working with global satellite communication companies like INMARSAT to develop a cost effective solution.

AirAsia is progressively implementing an in-flight Wi-Fi system that uses satellites and provides positional updates as a additional benefit. PK-AXC, the aircraft which crashed, had not been fitted as per this report in The Wall Street Journal.

Delayed ATC reaction

There is criticism in some quarters of the delays by Jakarta ATC in invoking emergency procedures. A full 40 minutes elapsed after the aircraft disappeared from radar and failed to responding to radio communications, before ATC invoked the first level of emergency, INCERFA. The United States FAA guidelines (read the document referenced in the chronology above) indicate INCERFA must be declared 30 minutes after loss of communication. Similar Jakarta ATC escalated to ALERFA 70 minutes after loss of communication against a specified 60. Jakarta ATC declared the highest level of emergency DETRESPA at 07:55L, 97 minutes after loss of contact, 25 minutes after the flight was scheduled to land at Singapore. While earlier escalation would not have prevented the crash, it may have allowed for earlier location of debris and remains which in turn would provide for more accurate location of the wreckage which would have not drifted in the strong currents of the Java sea.

What now?

Search and rescue vessels and aircraft are combing the Java sea trying to locate the remains and the wreckage, but a combination of bad weather, strong underwater currents, and poor visibility at the sea floor is thwarting the rescuers’ efforts.

What are the searchers looking for?

First and foremost, recovery of the remains of the persons on board the ill fated flight. After that the searchers will look for the main parts of the aircraft like the engines, the wings, and the fuselage, along with any other debris they can find. Locating the two “black boxes” i.e. the cockpit voice recorder (CVR) and digital flight data recorder (DFDR) is crucial. The CVR will let the investigators hear sounds from the cockpit for the last two hours of flight and help determine the reasoning behind the (in-)actions of the pilot(s). The DFDR measures upwards of 80 parameters and will allow investigators to re-create the flight in a virtual world. A forensic examination of the major sub-systems and debris will also help investigators determine the cause.

Who will be involved in the investigations

By protocol, the air safety agencies of the following countries are a part of the investigation team.
The country in whose geography the accident occurred takes the lead. In this case Indonesia.
The home country of the airline. In this case Indonesia.
The country in which the aircraft was manufactured. In this case France.
Any other country or organisation that is invited by the lead investigating agency. Organisations could include representatives of aircraft sub-systems manufacturers, insurance companies, media, etc.

What do investigation achieve

There is a common misconception that investigators try to assign blame. That is simply not the case. Investigators try determine the cause(s) of the accident with an intent to make recommendations to prevent such accidents occurring again. Most often air accident investigators are independent of the civil aviation regulator and make recommendations for the global body ICAO (international civil aviation organisation pronounced eye-kay-oh) and national regulators like the FAA, EASA, DGCA etc. to implement.

About Devesh Agarwal

A electronics and automotive product management, marketing and branding expert, he was awarded a silver medal at the Lockheed Martin innovation competition 2010. He is ranked 6th on Mashable's list of aviation pros on Twitter and in addition to Bangalore Aviation, he has contributed to leading publications like Aviation Week, Conde Nast Traveller India, The Economic Times, and The Mint (a Wall Street Journal content partner). He remains a frequent flier and shares the good, the bad, and the ugly about the Indian aviation industry without fear or favour.

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  1. Thanks Devesh – very informative!
    I did like the YouTube video and ATC recording you linked to. That is professionalism at its best.

    I would like to hear more about the prescribed reaction procedures when airplanes drop off radar. As you said, raising the emergency level 25 min after it was supposed to land is simply ridiculous. What do the regulations say?

  2. Rishad Minocher

    Well written, very well reasoned and informative Devesh! Echoed my thinking that there is far too much speculation in this case. An accident is just that – a combination of unfortunate circumstances and a thorough investigation is needed to arrive at the cause/s. Cheers.

  3. M. Azizul Islam

    Well done sir for a very well written and informative piece. I will link to i-Spot. Chees!

  4. Ian Glendinning

    Good analysis. Only point I would add / question is the idea that “the autopilot disengages and leaves the pilots to fly the plane”.

    My understanding, and part of AF447 loss, is that in the A3xx series aircraft, even with the autopilot disengaged, there is a lot of electronic “assistance” from the control system – eg stick-averaging if two pilots have the controls in their hands at the same time. And no doubt other fly-by-wire algorithms which may not be intuitive nor provide meaningful feedback about the state of control surfaces to the pilots, particularly if key sensors like airspeed and/or attitude are impaired.

    • Thanks for the suggestion, that is a good point. In the case of AF447, the failure of the three pitot tubes resulted the flight computers switching to alternate law which also removed a lot of the flight envelop protections, especially stall protection.

  5. Excellent article! Very informative and relevant. Thank you for this.

  6. Interesting read! I am of the opinion that any cause of the incident, whatever it is, did not cause the accident by itself. One minor anomaly can lead to one or more similar anomalies/failure and this chain of events eventually end up in a ‘collective set of events’ that render the flight situation catastrophic which also forces the aircraft to fail (lose control/disintegrate etc.).

    So I see no point in picking just one possibility for an air accident and analyzing its suitability for the ‘causation.’ It all depends on what initiated the catastrophic event and how one event led to other, eventually drowning the plane in the ocean. We need to remember, these set of events could have taken minutes or mere seconds.

    The findings of the investigation will tell us more to prepare for enhanced safety measures. Remember, any technological capability has a limit whi natural phenomena don’t have any. Just because we are confident on a technology doesn’t mean we’ll never face a greater anomaly.

    Here’s my analysis:

  7. I agree with your point, but in AA587 it was not weather that caused it.

    I am trying to dispel the fear generated in the mind of the average person when they listen to reports of certain sensationalist media who try and allude that a storm can break apart a plane.

  8. Hi Devesh, i’m just curious. What are the possible avionics failure for QZ8501? Could the weather radar on QZ8501 not effective in
    identifying the weather ahead? or anything like that