B737 Upset Recovery nose low high AoB
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B737 Upset Recovery nose low high AoB
Hi
Effectively a spiral descent with lots of energy available but why do the PLI's appear on during the recovery and we then have to respect not to pitch up too quickly.
Always good to ask a stupid question.
Regards
Pin
Effectively a spiral descent with lots of energy available but why do the PLI's appear on during the recovery and we then have to respect not to pitch up too quickly.
Always good to ask a stupid question.
Regards
Pin
I’m assuming in order not to over stress the airframe.
I’ve been told it’s Boeing’s philosophy that overspeeding is preferable over exceeding G limits.
Have not heard it from the horses mouth rather from sim instructors.
I’ve been told it’s Boeing’s philosophy that overspeeding is preferable over exceeding G limits.
Have not heard it from the horses mouth rather from sim instructors.
It might make sense as a read-across from the investigation into cross-over speed investigations after the rudder hard-over problems? The Boeing test flight analysis flights demonstrated the requirement to avoid any natural use of elevator to hold height, as it exacerbated the problem. Nothing whatsoever to back up that thought, just a first reaction.
The general design and certification principles would normally require an increase in stick force to minimise over-stressing the aircraft ('g' wt), similarly for higher speeds (Q).
The PLI is related to the stall margin defined by AoA, not solely at slow speeds but also at higher speeds with applied 'g'; PLI could be shown during a high speed / high 'g' turn (spiral dive).
Thus for a spiral dive recovery, levelling the wings should provide greater stall margin as 'g' is reduced - PLI moves up / disappears. With further pull up the speed could reduce, reducing the stall margin; thus PLI appears / repositions on the pitch scale - respect the PLI.
A dynamic situation involving speed, 'g', attitude and above all else AoA.
Beware rolling 'g', do not trim into a turn.
The PLI is related to the stall margin defined by AoA, not solely at slow speeds but also at higher speeds with applied 'g'; PLI could be shown during a high speed / high 'g' turn (spiral dive).
Thus for a spiral dive recovery, levelling the wings should provide greater stall margin as 'g' is reduced - PLI moves up / disappears. With further pull up the speed could reduce, reducing the stall margin; thus PLI appears / repositions on the pitch scale - respect the PLI.
A dynamic situation involving speed, 'g', attitude and above all else AoA.
Beware rolling 'g', do not trim into a turn.
PLI.........?
PLI - Pitch Limit Indicator; as per eckhard.
Origin was the indication of the maximum pitch attitude which is available to maximise climb performance in wind-shear; displayed on the attitude indicator.
The difference between aircraft datum (zero deg) and max pitch angle (PLI), is an indication of AoA margin for the intended use of PLI - normally stick-shake for wind-shear but over time systems and operations corrupt … …
The value of PLI - AoA margin, should reposition with change of speed, 'g'.
With more recent depictions / interpretations and switchable computations (EFIS / HUD); the PLI could indicate the wind-shear limit, EGPWS pull up, stall recovery, depend on aircraft type, operator procedures and training.
Similar to some EFIS speed tape low speed awareness symbology.
Origin was the indication of the maximum pitch attitude which is available to maximise climb performance in wind-shear; displayed on the attitude indicator.
The difference between aircraft datum (zero deg) and max pitch angle (PLI), is an indication of AoA margin for the intended use of PLI - normally stick-shake for wind-shear but over time systems and operations corrupt … …
The value of PLI - AoA margin, should reposition with change of speed, 'g'.
With more recent depictions / interpretations and switchable computations (EFIS / HUD); the PLI could indicate the wind-shear limit, EGPWS pull up, stall recovery, depend on aircraft type, operator procedures and training.
Similar to some EFIS speed tape low speed awareness symbology.
I wonder if PLI appears to remind you that rolling G can really hurt your aircraft?
As I recall it, retired 5 years now, Boeing says level the wings, then pull to raise the nose.
As I recall it, retired 5 years now, Boeing says level the wings, then pull to raise the nose.
Thanks guys.....
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The PLI appear to when in a low-speed scenario; You respect them so you don't end up in a stall. As mentioned above, rolling G can really hurt the aeroplane and its recommended to 'Unload the wings first', by doing this it reduces wing loading (increases stall margins) and lowers the AOA. Once the pitch is appropriate then you can roll the wings and adjust thrust accordingly.
If you don't respect the PLI during the recovery you will get the stick shaker.
If you don't respect the PLI during the recovery you will get the stick shaker.