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Accidents that Kill Helicopter Pilots

by Darren Smith, CFII

Helicopter Navigation:  Why Learn Helicopters | Costs | Private Pilot Helicopter | Commercial Pilot Helicopter | Glossary | Helicopter Lesson Guides Helicopter Ground School | SFAR73 | Accelerated IFR Rating 

Today, I'm fresh from the Robinson Safety Course in California.  During the 4 days of classroom training, my head was filled with stats, figures, and procedures.  On this dreary May morning, the weather isn't quite good enough to fly.  I figure I would write this article instead and share some of those good seminar details with fellow pilots.

Accident stats drive policies at training schools, dictate insurance rates, and now promulgate FARs.  A perfect example is the early accident stats in Robinson helicopters indicated that students got to solo too quickly.  They determined that 73% of all accidents involving their helicopters, 73% of those were during instructional use (dual and solo).  In an attempt to minimize solo accidents, which accounted for 18% of those instructional accidents, Robinson pushed for and got the SFAR which requires at least 20 hours of experience prior to solo.

As a result of the SFAR and the Robinson Safety Course, fatal accidents for recreational flying accounted for 60%, for hire 19%, instruction 19% and ferry flights 2%.  Of that 19% of instruction accidents, solo students accounted for 7% of fatal accidents, a serious reduction in the accident rate.  What caused all these instructional accidents?
  • Hovering too low (below 5 feet)
  • Flare too late and too low
  • Flying too low
  • CFI not on controls
  • Solo too early
  • Over confidence
  • People who just don't belong in the helicopter

Recreational flying

When it comes to recreational flying, there are four primary causes of fatal accidents.  They are wire strikes & collisions, weather, low RPM rotor stall, and Low G Mast Bumping.   Lets take a look at each of these areas and how we can avoid each accident type. 
The first type, wire strikes and collisions seem to defy logic.  But it sure makes sense because we all believe it can't happen to us.  Some people think this is a low time pilot problem.  But the accident stats tell the story:  these accidents happen to pilots of all experience levels.  Here are some tips for avoiding wire strikes and collisions:
  • As you fly, search for the poles and towers, not the wires.
  • When you find the towers, adjust the route to fly over the poles or towers
  • If you see a pole, assume there's a wire.  Dont even bother looking for the wires.
  • Flying over rivers are fun, but all rivers have wires crossing them.
  • If you want to fly low (like over a river), perform a good high and low recon.
  • If you fly at least 500ft AGL, you'll avoid most of the problems.  Below 500ft AGL, things may not be charted, marked, or lighted.
  • Before moving the helicopter, clear the area around and above you. 
Remember, hitting anything at sufficient height, you're dead.  Calilfornia Wire Strike Prevention Working Group says:
  • 85% occured when the ceiling is greater than 1000 feet
  • 66% involve pilots with more than 2500 flight hours
  • 40% of the pilots were aware of the wires
Weather caused 22% of the fatal accidents.  The primary reason was poor decision making.  Night, low visibility conditions frequently contributed to the fatality stats. Good pilots develop a set of personal minimums that guide the pilot in future decisions.  If the decision has already been made, later when weather is marginal, its easier to reject a flight because limitations have already been set. The Personal Minimums Checklist is a good guide for pilots to assist them in developing their own checklist.  Flying into IMC with any of the small helicopters is going to cause a loss of control accident within 7 seconds.  Remember, inadvertant IMC, you're dead.

Low RPM rotor stall which accounts for 14% of the fatal accidents has no recovery.  Letting the rotor get below 80% plus 1% for each thousand feet of altitude will cause low RPM rotor stall.  Overpitching the collective in such cases as high density altitude at full throttle will accelerate this likelihood.  Other pilots have accomplished this by rolling the throttle the wrong way on early helicopter models without the governor.  Sometimes pilots have even managed to overide the governor by squeezing the throttle so hard the governor was disabled (as its supposed to).  If you want to prevent low RPM rotor stall, learn how to recognize it.  The engine noise is be drastically lowered leading to an increase in vibration.  If that wasn't enough, the Low RPM light and horn will come on at 97%.   So there are plenty of warnings... there's the rotor warning horn plus 20% of rotor to decay before you get there, but should you succeed, your reward is instant death.   Simultaneously increasing the throttle, down collective, and aft cyclic is the proper recovery for low RPM rotor conditions.  Remember, below 80% (in a robbie), you're dead.

Rotor stalls can occur at any airspeed and it's more critical at altitude because you're likely to be at full throttle.  Another factor is the relationship between engine power to engine RPM.    If you want to get 100% of the rated horsepower out of the engine, you'll need to have rotor at full speed first.  See RHC Safety Notices 10 and 24 for further information. 

Low G Mast Bumping accounts for 7% of the fatal accidents.  It is very common on demonstration (discovery) flights and when the private pilot takes out his first passenger.  Mast bumping is the result of excessive rotor flapping and can occur due to to out of CG conditions and low G conditions. If excessive roll rates develop, the pilot may apply abrupt opposite cyclic.  As a result the mast is likely to be bumped if the rotor disk is not loaded (low G condition).

Robinson Helicopter History

R22 Standard SN 002-199 except SN175 1300LB gross weight Lycoming O-320
R22HP SN 1775 200-356 except SN256 SN301 SN350 SN351 Lycoming O-320
R22 Alpha 1983 SN 357-500 1370 gross weight Lycoming O-320
R22 Beta 1985 SN 501-2570 Lycoming O-320B2C  131hp for 5 minutes takeoff rating
R22 Mariner 1985 added the floats and the M on the serial number
R22 Beta II 1996 SN2561 and up now with a Lycoming O-360 180hp derated to 131hp/124hp
R44 prototype March 1990
R44 Astro December 1992 has electric trim
R44 Clipper fixed floats July 1996 pop-out floats June 1999
R44 Raven January 2000 with hydraulic controls
R44 Raven II October 2002 SN 10001 Lycoming IO-540 with fuel injection 245hp/205hp

Reader Comments

Date: Wed, 4 Apr 2007     Name = dirtyeddie
Comments = I saw the Robinson Safety class on video and it was a wake up call to me that flying a chopper no matter how fun it seems is serious business. I liked how Frank Robinson critiqued a wire strike accident saying, "This is how it usually happens...everyone is happy and having a great time and then Blammmo, a senseless tragedy unfolds". I'll never
forget what I saw or learned even If I never fly another day in a chopper. I find the below 80% rotor stall creepy. That and having 'till one one thousand to respond to an engine failure before you fatally stall the rotor of a 22. I'll bet in the real world 50% or higher hesitate. Finally the carb ice problem in the 22 should be done away with by fuel injection. It's too easy for pilots to forget to pull the knob one day. Again I appreciate you spending the time for us newbies. Props to you my friend!

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