Vy/Vx during windshear recovery and EGPWS recovery
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Vy/Vx during windshear recovery and EGPWS recovery
Dear Colleagues
I have a question regarding, which procedure to use during windshear/EGPWS recovery.
According to procedure on my current aircraft, EGPWS recovery is accomplished by performing a normal go around. This means flying at V2 with gear up, and an intermediate flap setting. The climb which is achieved is more or less a Vy climb. If necessary engines may be fire walled, if terrain is still closing.
Regarding EGPWS recovery, this is done by an "mutant" go aound procedure, in which aircraft configuration is maintained and the target speed is slightly above stick shaker speed, which must be below Vx (speed for maximum excess thrust).
In my world a windshear encounter should be counteracted by a Vy climb to gain maximum altitude over time. A EGPWS climb should be done at Vx to get maximum climb over distance.
Can anybody give an explanation?
Best regards
SE210
I have a question regarding, which procedure to use during windshear/EGPWS recovery.
According to procedure on my current aircraft, EGPWS recovery is accomplished by performing a normal go around. This means flying at V2 with gear up, and an intermediate flap setting. The climb which is achieved is more or less a Vy climb. If necessary engines may be fire walled, if terrain is still closing.
Regarding EGPWS recovery, this is done by an "mutant" go aound procedure, in which aircraft configuration is maintained and the target speed is slightly above stick shaker speed, which must be below Vx (speed for maximum excess thrust).
In my world a windshear encounter should be counteracted by a Vy climb to gain maximum altitude over time. A EGPWS climb should be done at Vx to get maximum climb over distance.
Can anybody give an explanation?
Best regards
SE210
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Windshear
Hi
I guess the cofusion is from "windshear" being EGPWS mode 7.
The correct action to be taken will depend on what aircraft you are operating and the warning given or conditions experienced.
I can only speak for my company and our SOP'S. We operate 737 efis.
If predictive windshear is active and "windshear ahead" warning is given, for example on the approach then a normal go around may be the preferred option if actual windshear is not experienced.
If windshear is experienced then the windshear recovery procedure is flown.
This procedure is very different from a normal go around.
1 Disconnect Autopilot
2 Press Toga and aggressively apply max thrust*
3 when max thrust is set disconnect auto throttle
4 roll wings level and pitch up to approx 15 degrees nose attitude
5 retract the speedbrake if extended
6 follow the flight director TOGA guidance
Note that apart from the speedbrake there is no change of config until clear of windshear.
Also note that airspeed is not to be chased. If you follow the fd's they may take you in and out of the stick shaker.
This is a very involved two crew operation with the non handling pilot playing a vital monitoring role, particularly with respect to vertical speed.
* If a terrain warning occurrs the firewall the thrust levers and head for sector safe!
Again other GPWS warnings associated with the different modes will, where neccessary make use of firewalling the thrust levers and keeping the existing config.
Hope this is of some help.
MN
The answer then is that in a windshear or egpws go around you will be right at the back of the drag curve trying to gain max height over min distance.
When considering even a normal go around I would of thought that Vy had little significance.
I guess the cofusion is from "windshear" being EGPWS mode 7.
The correct action to be taken will depend on what aircraft you are operating and the warning given or conditions experienced.
I can only speak for my company and our SOP'S. We operate 737 efis.
If predictive windshear is active and "windshear ahead" warning is given, for example on the approach then a normal go around may be the preferred option if actual windshear is not experienced.
If windshear is experienced then the windshear recovery procedure is flown.
This procedure is very different from a normal go around.
1 Disconnect Autopilot
2 Press Toga and aggressively apply max thrust*
3 when max thrust is set disconnect auto throttle
4 roll wings level and pitch up to approx 15 degrees nose attitude
5 retract the speedbrake if extended
6 follow the flight director TOGA guidance
Note that apart from the speedbrake there is no change of config until clear of windshear.
Also note that airspeed is not to be chased. If you follow the fd's they may take you in and out of the stick shaker.
This is a very involved two crew operation with the non handling pilot playing a vital monitoring role, particularly with respect to vertical speed.
* If a terrain warning occurrs the firewall the thrust levers and head for sector safe!
Again other GPWS warnings associated with the different modes will, where neccessary make use of firewalling the thrust levers and keeping the existing config.
Hope this is of some help.
MN
The answer then is that in a windshear or egpws go around you will be right at the back of the drag curve trying to gain max height over min distance.
When considering even a normal go around I would of thought that Vy had little significance.
Last edited by Major Nevitt; 15th Nov 2008 at 16:22. Reason: To Answer The Question
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Sorry about this. The question should have sounded like this
Vy/Vx during windshear recovery and EGPWS recovery
--------------------------------------------------------------------------------
Dear Colleagues
I have a question regarding, which procedure to use during windshear/EGPWS recovery.
According to procedure on my current aircraft, EGPWS recovery is accomplished by performing a normal go around. This means flying at V2 with gear up, and an intermediate flap setting. The climb which is achieved is more or less a Vy climb. If necessary engines may be fire walled, if terrain is still closing.
Regarding windshear recovery, this is done by an "mutant" go aound procedure, in which aircraft configuration is maintained and the target speed is slightly above stick shaker speed, which must be below Vx (speed for maximum excess thrust).
In my world a windshear encounter should be counteracted by a Vy climb to gain maximum altitude over time. A EGPWS climb should be done at Vx to get maximum climb over distance.
Can anybody give an explanation?
Best regards
SE210
Vy/Vx during windshear recovery and EGPWS recovery
--------------------------------------------------------------------------------
Dear Colleagues
I have a question regarding, which procedure to use during windshear/EGPWS recovery.
According to procedure on my current aircraft, EGPWS recovery is accomplished by performing a normal go around. This means flying at V2 with gear up, and an intermediate flap setting. The climb which is achieved is more or less a Vy climb. If necessary engines may be fire walled, if terrain is still closing.
Regarding windshear recovery, this is done by an "mutant" go aound procedure, in which aircraft configuration is maintained and the target speed is slightly above stick shaker speed, which must be below Vx (speed for maximum excess thrust).
In my world a windshear encounter should be counteracted by a Vy climb to gain maximum altitude over time. A EGPWS climb should be done at Vx to get maximum climb over distance.
Can anybody give an explanation?
Best regards
SE210
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Hi Major Nevitt.
I am current on the Q400 and also the RJ100.
In the RJ, the flight director will tell you what pitch to aim for during a windshear go around.
On the Q400 the flight director does not have this capability, and the procedure tells you to fly a speed just a fraction above the stick shaker activation speed.
My question is to which speeds to follow.
Cheers
SE210
I am current on the Q400 and also the RJ100.
In the RJ, the flight director will tell you what pitch to aim for during a windshear go around.
On the Q400 the flight director does not have this capability, and the procedure tells you to fly a speed just a fraction above the stick shaker activation speed.
My question is to which speeds to follow.
Cheers
SE210
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Hello again
I can offer no explanation why anybody would want to perform a Vy climb in windshear. rate of climb is a free gradient where as angle of climb is not. The whole point is to avoid terrain, gaining as much separation as possible in the shortest DISTANCE.
I can offer no explanation why anybody would want to perform a Vy climb in windshear. rate of climb is a free gradient where as angle of climb is not. The whole point is to avoid terrain, gaining as much separation as possible in the shortest DISTANCE.
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Hi SE210
I have no experience on either I am afraid.
This is an important issue so I would suggest asking a "friendly trainer."
When flying the RJ if the FD guidance is there then it should be followed but in the Q400 if it says just above the stick shaker then I wonder what instrumentation you guys have to tell you when you are just above it at that particular weight on that particular day? We are told that we may expect intermittent stick shaker during this situation.
Cheers
the major
I have no experience on either I am afraid.
This is an important issue so I would suggest asking a "friendly trainer."
When flying the RJ if the FD guidance is there then it should be followed but in the Q400 if it says just above the stick shaker then I wonder what instrumentation you guys have to tell you when you are just above it at that particular weight on that particular day? We are told that we may expect intermittent stick shaker during this situation.
Cheers
the major
SE210,
I think you'll find the reason is that both windshear and terrain avoidance maneuvers aim to give you the maximum rate of climb over a short duration as you are trying to overcome short term problems, e.g windshear or terrain ahead.
Vx and Vy give you best angle and rate of climb at a constant airspeed and therefore give you the best PROLONGED angle or rate.
You can, however, trade speed for height and achieve a greater angle and rate of climb, but only as long as you have airspeed to trade. THAT is why you pitch up to stick-shaker (or PLI in aircraft so equipped), on the basis that this should give you enough short duration "Zoom" to clear the terrain or maintain altitude through the windshear. If you still need to climb after that, obviously you can't pitch up any more as you'll stall, and pitching down will cause a short-duration decrease in performance, so all you can do is the best that stick-shaker speed will allow.
I think you'll find the reason is that both windshear and terrain avoidance maneuvers aim to give you the maximum rate of climb over a short duration as you are trying to overcome short term problems, e.g windshear or terrain ahead.
Vx and Vy give you best angle and rate of climb at a constant airspeed and therefore give you the best PROLONGED angle or rate.
You can, however, trade speed for height and achieve a greater angle and rate of climb, but only as long as you have airspeed to trade. THAT is why you pitch up to stick-shaker (or PLI in aircraft so equipped), on the basis that this should give you enough short duration "Zoom" to clear the terrain or maintain altitude through the windshear. If you still need to climb after that, obviously you can't pitch up any more as you'll stall, and pitching down will cause a short-duration decrease in performance, so all you can do is the best that stick-shaker speed will allow.
SE210, your question describes situations involving stabilised performance. In reality, the pull up manoeuvres will be able to use dynamic effects of excess energy, then slowing down to the stable conditions you describe.
The energy effect might have been of greater importance with a terrain encounter when using the older GPWS warning boundaries; some of this system’s limitations (and failed crew responses) resulted in accidents ‘near the top of hills’ etc due to late reaction or failure to use the excess energy. This might not be the case for EGPWS, but as the terrain encounter situation is not usually known, the same energy related manoeuvre should be used.
For windshear, most of the reactive warning systems use energy detection algorithms and energy management in the recovery guidance. It is still important to prevent ground contact, but also, the encounter may mean transiting adverse wind conditions; thus requiring a compromise between climb and speed through the conditions.
Recovery techniques may be a compromise which have to consider the worst case encounter and the realistic use of excess energy if available.
I suggest that you question the procedures in your manuals as they do not appear to match those elsewhere in the industry; see the extract from the Honeywell pilot guide:
The energy effect might have been of greater importance with a terrain encounter when using the older GPWS warning boundaries; some of this system’s limitations (and failed crew responses) resulted in accidents ‘near the top of hills’ etc due to late reaction or failure to use the excess energy. This might not be the case for EGPWS, but as the terrain encounter situation is not usually known, the same energy related manoeuvre should be used.
For windshear, most of the reactive warning systems use energy detection algorithms and energy management in the recovery guidance. It is still important to prevent ground contact, but also, the encounter may mean transiting adverse wind conditions; thus requiring a compromise between climb and speed through the conditions.
Recovery techniques may be a compromise which have to consider the worst case encounter and the realistic use of excess energy if available.
I suggest that you question the procedures in your manuals as they do not appear to match those elsewhere in the industry; see the extract from the Honeywell pilot guide:
Recommended response to EGPWS alerts are as follows:
1. Aggressively position throttles for maximum rated thrust. Apply maximum available power as determined by emergency need.
2. If engaged, disengage the autopilot and smoothly but aggressively increase pitch toward “stick shaker” or Pitch Limit Indicators (PLI) to obtain maximum climb performance.
3. Continue climbing until the warning is eliminated and safe flight is assured.
4. Advise ATC of situation.
1. Aggressively position throttles for maximum rated thrust. Apply maximum available power as determined by emergency need.
2. If engaged, disengage the autopilot and smoothly but aggressively increase pitch toward “stick shaker” or Pitch Limit Indicators (PLI) to obtain maximum climb performance.
3. Continue climbing until the warning is eliminated and safe flight is assured.
4. Advise ATC of situation.
