Learjet wrote:Downdraft induced accidents. Busting the Myth!
Looking through the CAA accidents stats one could be forgiven for thinking that "downdraft" related accidents only happen to gyros. In fact you'll struggle to find too many fix-wings or helicopter accidents directly attributed to downdrafts - but yet quite a few gyro accident reports mention encountering "a sudden and unexpected downdraft shortly after take-off" etc etc which resulted in the gyro executing a forced landing or prang. And yet we all brag about gyros having good wind tolerence attributes - so whats the deal with downdrafts? And why particularly so during / after take-off / climb?
Well, the truth is that there isn't really much of a deal about downdrafts. The problem is that when a gyro experiences a high rate of descent - to the pilot this may FEEL like being in a downdraft.
Especially if the reason for the high rate of descent isn't immediately clear.
And the CAA accident reports dutifully regurgitates this anecdotal speculation as actual fact. Which is a pity... beacuse I'll venture to say that a sudden and unexpected downdraft is seldom the real cause of a gyro mushing into the ground. (hence the lack of similar aerie, trikes and helo accidents due to downdrafts)
Neither is density altitude. Or excessive MAUW. Oh yes- they are definately dangerous contributing factors... but like these mysterious downdrafts, they are unlikely to be the sole cause but merely a link in the accident chain..
So what is the primary cause?
The answer(s) can be clearly found in the FAA Rotorcraft Flying Handbook... :
Failure to lift-off at proper speed
Failure to establish and maintain proper climb altitude and airspeed
and finally, when the airspeed drops sufficiently...
A gyroplane will DESCEND AT A HIGH RATE when flown at very low forward airspeeds. An unintentional high rate of descent can
also occur as a result of failing to monitor and maintain proper airspeed. In powered flight, if the gyroplane is flown below minimum level flight
speed, a descent results even though full engine power is applied. Further reducing the airspeed with aft cyclic increases the rate of descent.
At the point where maximum power available is being used, no further reduction in airspeed is possible without initiating a descent.
Welcome to flying behind the power curve.
Students are taught to fly by the numbers (which is fine in your average plane or heli) but because of the many variables (some typically unique to gyros)....ie. insufficient airspeed at lift-off in ground-effect, high angle of attack climb, using aft cyclic to climb rather than throttle, density altitude factors, take-off weight loadings etc etc... suddenly the numbers become very blurred as to exactly where this "getting behind the power curve" line is to be found in the flight envelope. Gyros don't have convenient stall warnings, or give the same impending stall signs (buffeting and sloppy controls etc) as per fixed-wing aeries. And anyway we were all told by the salesman that gyros don't stall. Perhaps so... but put them behind the power curve and they will fly only marginally better and descend just a bit slower than a falling brick.
Clearly this is an area where there is currently insufficient training by some gyro instructors. Behind the power curve flying... we need to emphasize how avoid it and how recognise its onset - and be drilled in how to recover from flying behind the power curve or inexperienced gyro pilots will continue to mistake it for being in a downdraft... and the ignorant CAA accident investigator will continue to regurgitate the 'sudden downdraft" story being told to them by the pilot who has just mushed his gyro into the ground.
So there it is. In my opinion the downdraft myth is busted.
The real culprit is behind-the-power-curve-ignorance and lack of training.
No doubt I'm going to come in for a bit of stick with these statements but it will be worth it if one gyro pilot out there encounters a "downdraft" and instead of pulling back on the stick in a vain attempt to get out of the clutches of the "downdraft" - and instead lowers the nose, increases airspeed and flies safely away from behind-the-power-curve (and the ground) it will have made his / her day. And mine!
