Why would a tailwind do this.......
Thread Starter
Why would a tailwind do this.......
Interesting reading about a recent 737-800 takeoff with a tail strike.
The investigation noted that a 10 knot tail wind increased the chance of a tail strike.
Why would this be the case?
The investigation noted that a 10 knot tail wind increased the chance of a tail strike.
Why would this be the case?
There are a few things to consider.
The first is that to take off a plane needs to have an airspeed matching the aircraft pitch. The lower the takeoff speed, the higher the required pitch.
The pitch is limited by the amount of rotation before the tail strikes the runway.
When there is a tail wind it takes longer to accelerate the plane to that airspeed.
The longer it takes to accelerate the more runway is required.
If the pilot has screwed up then they will run out of runway before they get to the minimum airspeed where the tail doesn't strike.
To make the screw up greater, the pilot who sees the runway running out will pull the plane to a higher pitch to take off at a lower airspeed - but that higher pitch is too high and the plane tail strikes the runway.
Look at a couple of limit cases. If there is a headwind equal to the no-tail-strike take-off speed the plane won't need any runway, just pull back on the controls and when the correct pitch is reached the plane takes off, with no runway roll at all. This trick has been done in light planes; maybe 30-40 knots. Alternatively, on a runway that is miles and miles long, with a sufficient tailwind that the airspeed is never positive, the airspeed required to take off is not reached because the tires cannot roll that fast.
The first is that to take off a plane needs to have an airspeed matching the aircraft pitch. The lower the takeoff speed, the higher the required pitch.
The pitch is limited by the amount of rotation before the tail strikes the runway.
When there is a tail wind it takes longer to accelerate the plane to that airspeed.
The longer it takes to accelerate the more runway is required.
If the pilot has screwed up then they will run out of runway before they get to the minimum airspeed where the tail doesn't strike.
To make the screw up greater, the pilot who sees the runway running out will pull the plane to a higher pitch to take off at a lower airspeed - but that higher pitch is too high and the plane tail strikes the runway.
Look at a couple of limit cases. If there is a headwind equal to the no-tail-strike take-off speed the plane won't need any runway, just pull back on the controls and when the correct pitch is reached the plane takes off, with no runway roll at all. This trick has been done in light planes; maybe 30-40 knots. Alternatively, on a runway that is miles and miles long, with a sufficient tailwind that the airspeed is never positive, the airspeed required to take off is not reached because the tires cannot roll that fast.
Thread Starter
The accident report did not indicate that runway was insufficient (although it may have been).
Lets assume a theoretical case where runway length was not limiting and the pilot did not rotate early or too much.
A simple steady state tailwind and a perfectly normal rotation rate and pitch attitude.
It still leaves me puzzled as to why the report stated that tailwind was a cause in this incident?
Lets assume a theoretical case where runway length was not limiting and the pilot did not rotate early or too much.
A simple steady state tailwind and a perfectly normal rotation rate and pitch attitude.
It still leaves me puzzled as to why the report stated that tailwind was a cause in this incident?
I presume you mean : https://www.mot.gov.sg/docs/default-...nal-report.pdf about B737-800, 9V-MGL
Tail Strike Event at Kathmandu Airport, Nepal?
I don't know why the report is written that way. They are very concerned with the overall mishandling of the plane and the post-strike response by the crew.
They do note "The aircraft was operating close to its maximum take-off performance limit and the take-off configuration used was Flap 1 without using engine bleeds" which would mean a tailwind would have an adverse effect on the ability to leave the runway. They also mention it is surrounded by unfavorable terrain so leaving the runway is just one consideration that requires a healthy vertical velocity component.
I'd ask, would a headwind of 10 knots have allowed the plane to lift off before getting beyond the pitch limit? If so, then a tailwind of the same magnitude would be detrimental in a notable amount. The report indicates a general local wind of 8 knots tending to be a headwind was reported. That calculated tailwind is -18knots off of that.
Tail Strike Event at Kathmandu Airport, Nepal?
I don't know why the report is written that way. They are very concerned with the overall mishandling of the plane and the post-strike response by the crew.
They do note "The aircraft was operating close to its maximum take-off performance limit and the take-off configuration used was Flap 1 without using engine bleeds" which would mean a tailwind would have an adverse effect on the ability to leave the runway. They also mention it is surrounded by unfavorable terrain so leaving the runway is just one consideration that requires a healthy vertical velocity component.
I'd ask, would a headwind of 10 knots have allowed the plane to lift off before getting beyond the pitch limit? If so, then a tailwind of the same magnitude would be detrimental in a notable amount. The report indicates a general local wind of 8 knots tending to be a headwind was reported. That calculated tailwind is -18knots off of that.
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Different wind at each end of the runway. Accelerate with calm wind, rotate, go into tailwind, and the pitch attitude will increase while lift is lost, degrading margins to tail strike.
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Don't know aerodynamics of lift during rotation but there's a general feel about the rotation like the ground speed and rate of change of attitude. In TW the GS is higher which could create illusion that rate of rotation is slower and make pilot inadvertently increase rate of rotation. There's a tail strike pitch for each aircraft that needs to be monitored during rotation and if approaching that without lift off then you need to freeze rotation.
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There are a few things to consider.
When there is a tail wind it takes longer to accelerate the plane to that airspeed.
The longer it takes to accelerate the more runway is required.
If the pilot has screwed up then they will run out of runway before they get to the minimum airspeed where the tail doesn't strike.
To make the screw up greater, the pilot who sees the runway running out will pull the plane to a higher pitch to take off at a lower airspeed - but that higher pitch is too high and the plane tail strikes the runway.
Look at a couple of limit cases. If there is a headwind equal to the no-tail-strike take-off speed the plane won't need any runway, just pull back on the controls and when the correct pitch is reached the plane takes off, with no runway roll at all. This trick has been done in light planes; maybe 30-40 knots. Alternatively, on a runway that is miles and miles long, with a sufficient tailwind that the airspeed is never positive, the airspeed required to take off is not reached because the tires cannot roll that fast.
When there is a tail wind it takes longer to accelerate the plane to that airspeed.
The longer it takes to accelerate the more runway is required.
If the pilot has screwed up then they will run out of runway before they get to the minimum airspeed where the tail doesn't strike.
To make the screw up greater, the pilot who sees the runway running out will pull the plane to a higher pitch to take off at a lower airspeed - but that higher pitch is too high and the plane tail strikes the runway.
Look at a couple of limit cases. If there is a headwind equal to the no-tail-strike take-off speed the plane won't need any runway, just pull back on the controls and when the correct pitch is reached the plane takes off, with no runway roll at all. This trick has been done in light planes; maybe 30-40 knots. Alternatively, on a runway that is miles and miles long, with a sufficient tailwind that the airspeed is never positive, the airspeed required to take off is not reached because the tires cannot roll that fast.
Don't know aerodynamics of lift during rotation but there's a general feel about the rotation like the ground speed and rate of change of attitude. In TW the GS is higher which could create illusion that rate of rotation is slower and make pilot inadvertently increase rate of rotation. There's a tail strike pitch for each aircraft that needs to be monitored during rotation and if approaching that without lift off then you need to freeze rotation.
Last edited by punkalouver; 20th May 2023 at 02:57.
Here's another incident:
The tailstrike was the result of an excessive rate of rotation during the takeoff. This was exacerbated by a variable headwind component which contributed to a lift off speed that was lower than intended by the manufacturer and compounded the loss of tail clearance.
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Vr speed is based on IAS. Assuming in both headwind and tailwind situations the Vr is the same, the aircraft should behave exactly manner aerodynamically (time to lift off, pitch at lift off.. etc) if both takeoffs are done precisely the same way. The only difference here is the resultant groundspeed - in a tailwind more ground covered. I do not think there is an increase risk of tailstrike as well in a tailwind situation. Unless we are talking about a sudden lost of headwind component (sudden reduction in HW or increase in TW) during rotation, resulting in the IAS and thus lift to decrease at this moment especially with the aircraft at its take-off performance limits and the pilot keeps pulling back.
Unless we are talking about a sudden lost of headwind component (sudden reduction in HW or increase in TW) during rotation, resulting in the IAS and thus lift to decrease at this moment especially with the aircraft at its take-off performance limits and the pilot keeps pulling back.
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Just to be clear, taking off in a tailwind does not increase the risk of a tailstrike.
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It's clearly concluded that Tail strike happened due to faster rate of rotation and reaching an attitude beyond tail clearance attitude. The discussion is about did prevailing tail wind as suggested facilitate that?
The thing I can imagine happening with a strongish TW vs the more normal HW in combination with a heavy AC is the ground speed will be much higher, and that sight picture might have led the pilot to make an inappropriately large ANU input.
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Don't folks rotate jets with reference to the A/H these days ? ... especially on Types which have a liking for tail strikes. I was brought up on the Boeing three holer and the A/H reigned supreme during the lift off rotation sequence.
Just stating the obvious: Steady state tailwinds won't change anything about the rotation from a physic's point, and changing wind conditions apply the same to HW as they do to TW.
The thing I can imagine happening with a strongish TW vs the more normal HW in combination with a heavy AC is the ground speed will be much higher, and that sight picture might have led the pilot to make an inappropriately large ANU input.
The thing I can imagine happening with a strongish TW vs the more normal HW in combination with a heavy AC is the ground speed will be much higher, and that sight picture might have led the pilot to make an inappropriately large ANU input.
Historically, tail strikes are over-represented in crosswinds and tailwinds, due to pilot input, and not the conditions themselves. An increase in tailwind component (TWC) will result in a higher pitch attitude required to fly off the ground, and as most often the crew are not scanning the airspeed indicator, (ASI, AS, or MASI), then an increased TWC at the point of rotate will reduce tail-ground clearance at liftoff. Most cases but not all tail strikes I have investigated occur immediately after the wheels come off the ground, although the total events were pretty evenly distributed between takeoff and landing cases. The control inputs are usually found to be more abrupt and larger displacement than a zero wind or simple headwind case. Humans are curious creatures. In almost all transport category aircraft, a rotate commenced at the correct speed and rate will result in V2 being achieved immediately before the wheels come off the ground, when operating a multiengine aircraft without a power loss, yet we removed the call of achieving V2 around 1990... and loss of tail clearance events increased.
There are several documents out there worth reading, the main ones being:
“Preventing Tail Strikes at Takeoff” by Airbus
“Tail Strike Avoidance” by Boeing
“Tail Strikes: Prevention” by the Chief Pilot of Boeings Flight Ops Safety Department
Between Airbus and Boeing the causes of tail strikes include:
Early Rotation
Incorrect Rotation Technique
Incorrect configuration
Incorrect CG calculation or stab setting
Oleo under inflation
Improper use of flight director
Mis handling during gusty winds and crosswinds
No where is it suggested that tail wind is a contributor.
The most significant is gusty wind, wind shear and crosswind.
A headwind gust can contribute to a tail strike in the same way that a tail wind gust can.
“Preventing Tail Strikes at Takeoff” by Airbus
“Tail Strike Avoidance” by Boeing
“Tail Strikes: Prevention” by the Chief Pilot of Boeings Flight Ops Safety Department
Between Airbus and Boeing the causes of tail strikes include:
Early Rotation
Incorrect Rotation Technique
Incorrect configuration
Incorrect CG calculation or stab setting
Oleo under inflation
Improper use of flight director
Mis handling during gusty winds and crosswinds
No where is it suggested that tail wind is a contributor.
The most significant is gusty wind, wind shear and crosswind.
A headwind gust can contribute to a tail strike in the same way that a tail wind gust can.
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Bottom line..,,,rotate at the proper rate for your aircraft and if anything, do it at a slightly lower rate on gusty days. Assuming no major mistakes such as mis-configuration, speed, wind calculation, or thrust setting errors, things will be fine.
I suspect the tail strikes that happen due to early rotation speeds are where the tail strike pitch attitude is approached with wheels still on the ground but the rotation is continued. If one were to stop the rotation early because they had sensed that the aircraft was not getting airborne, they could prevent the tailstrike and wait for the aircraft to accelerate to a safer speed which is a good reason to be aware of the tailstrike pitch attitude on your aircraft type.
Perhaps the above is easier said than done. I have never tried early rotation in the sim, but it might be an interesting exercise.
I suspect the tail strikes that happen due to early rotation speeds are where the tail strike pitch attitude is approached with wheels still on the ground but the rotation is continued. If one were to stop the rotation early because they had sensed that the aircraft was not getting airborne, they could prevent the tailstrike and wait for the aircraft to accelerate to a safer speed which is a good reason to be aware of the tailstrike pitch attitude on your aircraft type.
Perhaps the above is easier said than done. I have never tried early rotation in the sim, but it might be an interesting exercise.
Last edited by punkalouver; 26th May 2023 at 12:21.
