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Old 05-24-2011, 08:12 AM
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APC225
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Originally Posted by Sniper View Post
The devil is in the details, of course.

If you don't know exactly where your thrust levers were (Airbus sets a 'max power available to the autothrust' detent, and the TL's stay there), and didn't make a mental note of the exact pitch (on the PFD) and power (EPR, N1, or what have you on the ECAM) you needed in that specific configuration, it can be very hard to fly a heavy aircraft @ high altitude due to the 'coffin corner' issues.

For AF447, the max altitude was almost certainly limited by the weight of the aircraft, so they were likely flying close to (or at) their max altitude while still maintaining their margins (1.3 - 1.6 Vso, depending on what AF uses or what Airbus has auto-programmed) while waiting to burn down to their next climb weight. In turbulence, it is hard to see what exactly your required pitch and power #'s are if the automation is constantly changing them to adapt to the turbulence. Then to unexpectedly pick up an airspeed failure with a simultaneous autopilot and auto throttle disconnect . . . max performance altitude, turbulence reduced margins, unexpected failures, no visual horizon, colorful radar picture - not just another day @ the office.

This accident may highlight one of the main disadvantages of the 'airbus set-up' - there is no physical way to monitor the control inputs of the automation. With a Boeing, you can watch the thrust levers and the yoke move - if they start to move in an unexpected manner, the automation kicking off not only isn't quite as unexpected, but you know the approximate thrust lever angle and relative yoke position you had prior to the 'situation', and can use those positions as a starting point in your recovery. With the Airbus, you have no physical reference to start from.

Hopefully, once the final report comes out, we can all learn something from it.
One can only hope the FAA takes note of the envelope issues you outline and make some rules governing flying in this regime. I'm weary of guys wanting to climb to max altitude to "get over a thunderstorm" or when other A/C are reporting mountain wave. A 12 knot spread between min and max speeds is just stupid.
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