Pitch Authority

[Chris Scott]

Go-Around

To develop the argument a bit:

In most cases, the problem arises when the all-moving horizontal stabiliser (tailplane) is delivering a pitch moment in the opposite direction to what the pilot needs for the new thrust setting. The elevator authority can then sometimes be insufficient.

One example of this, on a conventional jet transport, is a go-around from VREF at full flap. The pilot (or AP) has to push like mad, while simultaneously trimming the stabiliser from a very high pitch-up-trim setting to a more neutral one.** If the speed has been allowed to get below VREF, loss of pitch control may result. In older types, it was possible to "stall" the stabiliser motor, because of the enormous aerodynamic forces involved as the elevators oppose the stabiliser.

Fortunately, it should usually be possible to recover by reducing thrust a bit...
[Unfortunately, perhaps, SOPs usually demand that GA thrust is maintained until a certain height above the airfield, even though this usually gives far more performance than necessary. Airbus (FBW) FMGCs do not reconfigure from Approach mode to Go-Around mode unless TOGA thrust is selected (i.e., pushing the throttles fully forward). However, this does not physically prevent the pilot from immediately throttling back to a lower thrust setting, e.g., Climb thrust.]


** Airbus FBW
In the non-autopilot case, this necessity for the pilot to push and trim forward does not apply in Airbus FBW types, even though they are of a similar configuration aerodynamically. Once the pilot has rotated to the go-around attitude, the appropriate amount of down elevator will be selected by the FBW system, with the side-stick neutral. At the same time, the system will auto-trim the THS (trim-able horizontal stabiliser), rather like CWS systems on some 1970s aeroplanes. The only indication of the down-elevator will be on the F/CTL page of ECAM.