Originally Posted by
mm43
Now don't let the facts get in the way of a good story.
BEA Interim Report No.2
We know from the AOC positions that the aircraft was proceeding at M0.82 and at what seemed a constant GS of 467KTS. However, when changing to Alt Law the last valid airspeed data caused the RTLU to limit rudder angle to +/-7.9°. A higher level, e.g. FL362 would also provide the same CAS, and I am sure that HN39 will be able to come up with a suitable graph for higher levels.
In all probability the a/c was still at FL350 and had slowed slightly in "light chop". We don't really know, and the RTLU may be telling us something different, so is this another "red herring" or something that should be considered.
We do not yet know actual height, air temperature, windspeed or Mach No. Ground speed is not that precise as the exact time of transmission seemed to vary, apparently slipping by 15 seconds occasionally.
Flight plan was for FL370 M0.82, but would have needed approval to shift to FL370 from FL350. Recommended Mach number for Turbulence Penetration lower (M0.8 or M0.78?).
The BEA statement on RTLU very careful, and correct according to the figure posted by mm43
http://www.pprune.org/tech-log/44963...ml#post6411873
My use of online calculator generates 272KCAS from
M0.80 @ 35,000ft ISA +15 deg C
M0.82 @ 36,200ft ISA +15 deg C
M0.84 @ 37,400ft ISA +15 deg C
M0.86 @ 38,600ft ISA +15 deg C