Hi , just want some thoughts on the following situation. This has resulted in the captain being demoted to FO, and myself (the FO) being suspended from flying for one month with no pay, so to us guys its a pretty serious issue and any thoughts or comments as to is the blame ours, some environmental impacts such as wind changes, aircraft not behaving normally etc.
We were cruising at 38100 feet (China) and the aircraft was a 737-800. The FO (myself was pilot flying)
- Descended to 33100 feet 1000 feet per minute using VNAV descent. Then maintained altitude until we were 2000 feet plus above the descent path (captains memory) 1000plus feet above descent path (my memory) not sure of the exact amount.
- Told to descend and started descent using VNAV, at this time we had a tail wind component of -25 knots and speed of Mach .78
- Drag required warning came on the FMC, relayed to the captain who said no need for speed break because so close to descent path. For previous experience I did not see a problem. I then entered some descent information on the FMC. Looked up and saw a rapidly (very rapidly) increasing green speed trend arrow. Which resulted in a Mach over-speed warning.
- The following is from QAR and our actions.
- At 40 seconds after beginning decent vertical speed was 5400 feet/Min (we know its fast) with a pitch down of 5.6 degrees, speed Mach .784 . Tailwind component 25 knots. This is probably about the time I noticed the speed trend arrow and called to the captain “speed” or something to that affect.
- then aircraft started to pitch up reaching .527 degrees nose down
- At 42 seconds after the decent began the speed break was deployed. At that point the aircraft maintained the same pitch down rate of .527 for 4 seconds and the vertical speed actually increased by 400 feet per minute and the airspeed also increased.
- Then the aircraft started to pitch up, but due to momentum the air speed still increased, but at a slower rate.
- At 46 seconds after the decent began VS was engaged by the FO and a low decent rate dialled up.( this does not show on the QAR but both captain and FO agree it happened.
- AT 47 seconds after the decent began the captain selected level change.
- At 50 seconds after the decent began , at 29740 feet we had the Mach over speed warning sound at Mach 8.26, with a decent rate of 3400 feet per minute
- At 51 seconds the speed was Mach .831 before the speed and descent rate rapidly reduced and the flight continued. The warning sounded for 6 seconds, with us being over speed for 2 seconds and equal to the speed for one second.
Wind for the first 40 seconds was steady and gave us an effective tail wind of 25 knots. At 40 seconds this rapidly changed to a tail wind component of 45 knots in less than 20 seconds. We think the wind change contributed quite a lot to the overall situation.
Any thoughts, especially anything useful we can use in our defence. Also if the blame is totally ours then that something we have to accept. Thanks