Videos of LTE?
Join Date: Feb 2005
Location: KPHL
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Madrid Video
Listen to the internal video. At the 50 second mark (approximately 8 seconds after take off) there is a distinct change in high frequency noises. I'm guessing an engine failure, partial power, or governor low side (or whatever you call it where you live).
Now look at the external video at 8 seconds following take off. No noticeable (to me) change in altitude. There was a slight change in sound but I couldn't convince myself if it was consistent with a power loss. The aircraft had started moving forward, towards an obstacle.
Put yourself into the cockpit and don't assume you have immediate, alerting, and clear indications of what is happening. What would you do? In hindsight, recovering to the landing is the right thing to do. However, you don't know what is going on immediately, you have passengers in suits taking off from a bull fighting arena with lots of media/video cameras running. I'd say a bit of pressure could exist. That's no excuse for leading to an accident, but it is a reality.
By the time a power problem is evident, you're over the seats with a reducing Nr, and a tail rotor becoming increasingly ineffective.
Play it backwards and find out how to avoid this in the future. Departing over an obstacle with minimal vertical clearance and without OEI flyaway capability is asking for it. Reduce weight, find a different departure path, or fly a profile that allows OEI reject/flyaway.
Of course, all this is based on my assumption that there was a power loss.
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As far as the tail rotor issue, we're going down a road that happens so often when discussing helicopters. Terminology is not very consistent, and where it is there is a great deal of misunderstanding. Whatever you want to call it, the tail rotor wasn't providing enough thrust to prevent the yaw. Of course, that doesn't help in preventing further incidents.
The way LTE was explained to me, is that it occurs in conditions where you should (or did) have enough authority, but a disturbance of the air suddenly changes that. There were many conditions such as a wind that places tip vortices of the main rotor into the tail rotor, crosswinds of a certain speed range/direction, etc.
I've experienced what was called LTE in a 206 during a demonstration. Hovering sideways into the wind, increasing groundspeed. The yaw control started getting difficult, then suddenly a large yaw rate developed. My instinct was to put in a large correction, but I was briefed not to. After a small rotation (guessing about 20 degrees) the yaw rate began to reduce and the frozen pedal position (with plenty of margin) was sufficient to maintain the hover heading.
Every helicopter I've flown does have certain relative winds where the yaw control becomes more difficult, but most don't suddenly generate rapid yaw rates.
Now I'm going to open myself up to criticism. Some helicopters enter VRS smoothly and easily, and require pilot effort to get out. Other helicopters appear to enter VRS, pitch and roll for a bit, then stabilize. If a tail rotor went into VRS (horizontally)smoothly and easily, then it would appear as a sudden loss of effectiveness of the tail rotor. If the tail rotor appeared to enter VRS, but then dropped out on its own, it would create difficult yaw control for the pilots.
This is why I believe LTE is a valid term. It probably isn't used properly all the time, but the preceeding paragraph does explain a situation where you have sufficient power, you have sufficient control margins, but then with the right conditions you can suddenly find yourself without sufficient anti-torque.
Is this a design problem? I say yes. Flying within the approved envelope of the helicopter, I don't think this should happen. If it passes certification that doesn't mean its a corrupt manufacturer or that its not a design problem, just that the criteria for certification don't cover everything.
Matthew.
Now look at the external video at 8 seconds following take off. No noticeable (to me) change in altitude. There was a slight change in sound but I couldn't convince myself if it was consistent with a power loss. The aircraft had started moving forward, towards an obstacle.
Put yourself into the cockpit and don't assume you have immediate, alerting, and clear indications of what is happening. What would you do? In hindsight, recovering to the landing is the right thing to do. However, you don't know what is going on immediately, you have passengers in suits taking off from a bull fighting arena with lots of media/video cameras running. I'd say a bit of pressure could exist. That's no excuse for leading to an accident, but it is a reality.
By the time a power problem is evident, you're over the seats with a reducing Nr, and a tail rotor becoming increasingly ineffective.
Play it backwards and find out how to avoid this in the future. Departing over an obstacle with minimal vertical clearance and without OEI flyaway capability is asking for it. Reduce weight, find a different departure path, or fly a profile that allows OEI reject/flyaway.
Of course, all this is based on my assumption that there was a power loss.
------------------------------
As far as the tail rotor issue, we're going down a road that happens so often when discussing helicopters. Terminology is not very consistent, and where it is there is a great deal of misunderstanding. Whatever you want to call it, the tail rotor wasn't providing enough thrust to prevent the yaw. Of course, that doesn't help in preventing further incidents.
The way LTE was explained to me, is that it occurs in conditions where you should (or did) have enough authority, but a disturbance of the air suddenly changes that. There were many conditions such as a wind that places tip vortices of the main rotor into the tail rotor, crosswinds of a certain speed range/direction, etc.
I've experienced what was called LTE in a 206 during a demonstration. Hovering sideways into the wind, increasing groundspeed. The yaw control started getting difficult, then suddenly a large yaw rate developed. My instinct was to put in a large correction, but I was briefed not to. After a small rotation (guessing about 20 degrees) the yaw rate began to reduce and the frozen pedal position (with plenty of margin) was sufficient to maintain the hover heading.
Every helicopter I've flown does have certain relative winds where the yaw control becomes more difficult, but most don't suddenly generate rapid yaw rates.
Now I'm going to open myself up to criticism. Some helicopters enter VRS smoothly and easily, and require pilot effort to get out. Other helicopters appear to enter VRS, pitch and roll for a bit, then stabilize. If a tail rotor went into VRS (horizontally)smoothly and easily, then it would appear as a sudden loss of effectiveness of the tail rotor. If the tail rotor appeared to enter VRS, but then dropped out on its own, it would create difficult yaw control for the pilots.
This is why I believe LTE is a valid term. It probably isn't used properly all the time, but the preceeding paragraph does explain a situation where you have sufficient power, you have sufficient control margins, but then with the right conditions you can suddenly find yourself without sufficient anti-torque.
Is this a design problem? I say yes. Flying within the approved envelope of the helicopter, I don't think this should happen. If it passes certification that doesn't mean its a corrupt manufacturer or that its not a design problem, just that the criteria for certification don't cover everything.
Matthew.
