QZ8501: The Trajectory

Throughout the first week of the accident, amidst the speculation and mad schedules, I received from various sources leaks of the aircraft trajectory based on the ADS-B replay data. A projection with more details than the one issued by the government is shown above.

Me and several colleagues who spent many hours looking into the ADS-B data are committed to not disclose the actual replay of the original ADS-B data, to respect the process undertaken by the Indonesian National Transportation Safety Committee. The projection above was also only disclosed publicly after the goverment decided to issue a less detailed projection:

What can we decipher from the ADS-B data?

1. The aircraft was cruising “normally” at FL320.
2. At 23:16:52, the aircraft began to turn left, with a slight drop in altitude and shown by the vertical speed.
3. After turning left further, at 23:17:29, the aircraft reached a maximum vertical climb rate of 12,675ft per minute, passing FL351, and a ground speed of only 311.57kts.
4. At 23:17:43, the aircraft began to turn left again and had just passed it’s maximum altitude and was recorded at FL373, and began to drop at a rate of -894ft per minute and a ground speed of only 169.19kts.
5. At 23:18:03, the aircraft made a sharper turn to the left, dropping through FL327, at a rate of -20,000ft per minute, and a ground speed of only 119.09kts.
6. After continuing south east for a about half a minute, the aircraft began to turn left again at 23:18:45, passing through it’s last valid altitude at FL235, with a descent rate of -15,681fpm and a ground speed of a mere 78kts.
   
7. The aircraft continued a tight left turn and was last detected at 23:19:46 with a ground speed of just 68kts.

From the trajectory, we can conclude the following:

1. The aircraft flight control law must have degraded from Normal Law in order for the aircraft to depart the protected flight envelope.
2. The climb rates are possible because of the consequential loss in forward speed. This negates the theory of updrafts.
3. The aircraft would not have gone very far from the last point of contact, given the speed and descent rate. A recovery out of the stall into normal flight was extremely unlikely.
4. The impact would have been one of high vertical rate, with low forward speed, and a relatively level to nose up aircraft body attitude, similar to Air France 447, but the roll angle is anyone’s guess.

What remains unknown from the trajectory information:

1. What caused the flight control system reconfiguration.
2. Who was the pilot flying? The Captain or the First Officer
3. What was the trajectory below FL235.

Thankfully, on 29 January 2015, the Indonesian National Transportation Safety Committee had released some information regarding to the factual aspect of the accident.