Originally Posted by
RifRaf3
"a safer reaction to overspeed would be to apply speedbrakes/reduce thrust, instead of raising the aircraft's nose"
In most airliners they are not speedbrakes, but spoilers. Fighters generally have speedbrakes. Spoilers reduce lift as well as increase drag. Hence in airliners they are generally only used on descent when reduction in lift is required and not in level cruise or climb as they reduce stall margins. In the rare event of an overspeed trend in level flight at altitude, you reduce thrust first and only then consider using spoilers. This was not an overspeed situation but a nose up pitch with reducing airspeed.
The automatics could have thought it was overspeed.
Enter a warm air with a spike
up in outside air temperature and the Airbus protections can give you a zoom climb. If that warm air is warm because it is an updraft of significant strength the zoom plus updraft speed could lead to an impressively rapid gain in altitude.
It is what actions are taken by the crew and the subsequent changes in air temperatures, wind changes and downdrafts that will decide what happens to the aircraft. From previous posts on this and AFR447 thread it would appear setting pitch and power for cruise (if the automatics will let you) is the best strategy. And from memory of previous posts this includes stop the trim doing whatever it is doing and manually override it to set what is required, push forward on the stick more than half way to break out of an Alpha prot zoom etc etc., These all appear actions to prevent the aircraft automatics causing issues.
See this report
The A340 crew received a TCAS TA at 14:09 hrs (A340 clock time) alerting them to the proximity of
the A330. At 14:20:40 hrs the aircraft entered a region of successive and increasing variations in wind
and air temperature, which in turn caused fluctuations in pitch angle, normal g, altitude, calibrated
airspeed, engine N1% and Mach number. One minute later in a particularly vigorous fluctuation, the
aircraft’s Mach number briefly increased to 0.87. This speed excursion above the Mach 0.86 limit
triggered a Master Warning at 14:21:40 and automatically disengaged the autopilot. One second later
the TCAS issued an RA with a “DESCEND, DESCEND, DESCEND”audio warning. In the two second
period after the initial speed excursion above Mach 0.86 the Mach number decayed to 0.855 and then
increased again to 0.882. It remained above 0.86 for two seconds before decreasing and remaining
below 0.86 for the remainder of the turbulence encounter.
Five seconds after the autopilot disengaged, the thrust levers were closed and then the autothrust was
disconnected, probably by the handling pilot in an effort to prevent another overspeed condition. Ten
seconds after the autopilot disengaged, the corrected or phase-advanced angle of attack (a computed
parameter which is not recorded but can be calculated by Airbus Industrie from the DFDR data) reached
the ‘alpha prot’ value. This angle of attack excursion beyond alpha prot caused a change in the pitch
flight control law from normal law (NZ law) to angle of attack protection law (AoA law). If both
sidesticks are at neutral, the AoA protection law seeks to hold the angle of attack constant at alpha prot
until a sidestick pitch command is made. If the stick is pulled fully aft then the angle of attack increases
to alpha max. If the sidestick is not moved aft, AoA protection law remains active until a nose-down
command greater than half forward travel is made or until a nose down sidestick input has been applied
for more than one second. The first recorded sidestick input was made at 14:22:08 which was some 28
seconds after the commencement of the Master Warning.
For 18 seconds after the autopilot disengaged the aircraft remained within 200 feet altitude of FL 360
but once AoA law was invoked at 14:21:50 hrs, the aircraft’s attitude began to pitch nose-up. The pitchup
trend continued for 17 seconds reaching a peak of 15° nose-up shortly before the first nose-down
sidestick command was applied. Throughout this phase the aircraft climbed rapidly (reaching a peak
rate of about 6,000 ft/min) due to the increase in lift created by the flight control system’s capture of
alpha prot. The aircraft reached its apogee at FL 384 at 14:22:28 hrs where the airspeed had decayed to
205 KIAS and 0.67 Mach even though full thrust had been applied.
Page 11 of:
http://www.aaib.gov.uk/cms_resources...%2006-2001.pdf
So what happens at FL380 and 205KIAS/Mach 0.67 15deg nose up, if full thrust is applied and there is compressor stall on the left hand engine? You now have full thrust on the right engine and drag from the left engine. IMC in a grey goldfish bowl with severe turbulence is not a time to be the
first pilot to flight test the aircraft's '
spin tolerance' with the aircraft helpfully playing all the various cavalry charges and stall warnings sufficient that you cannot hear each other.