User:Msiddalingaiah/Helicopter crash

A student pilot with no helicopter experience attempts to solo. The spectacular Windows Media video clip is here. Fortunately, no one was hurt.

Transcript

Here's a transcript of the audio at the end:

Observer:

What's goin' on Jim? What's the matter with this guy, huh?

Camera man:

Uh, he's just learning how to fly this helicopter -- he hasn't had any time in it. He just bought it -- he owns the helicopter and he just ate the big one. He was told not to fly this thing I believe and...

Observer:

He been checked out in (unintelligable)?

Camera man:

No, I don't think so, not at all.

Camera man:

(unintelligable) are you all right?

Observer:

Watch out

Camera man:

(unintelligable) get away from that thing! Just get away from it!

NTSB Report

The full report is here. Here is the summary:

A HUGHES 269B WENT OUT OF CONTROL AND COLLIDED WITH THE GROUND DURING A T/O TO A HOVER. THE PILOT HAD PURCHASED THE AIRCRAFT RECENTLY AND WAS LEARNING TO FLY IT. HE WAS SCHEDULED FOR HIS FIRST FLIGHT LESSON ON THE DAY OF THE ACCIDENT. THE CFI REPORTED THAT HE HAD TOLD THE STUDENT PILOT TO WAIT FOR HIM AND NOT TO TOUCH ANYTHING. WHILE WAITING FOR THE FLIGHT INSTRUCTOR, THE NON ROTORCRAFT RATED STUDENT PILOT STARTED THE AIRCRAFT, RAN IT UP TO FULL RPM, AND THEN BEGAN TO INCREASE THE COLLECTIVE PITCH CONTROL. THE HELICOPTER CLIMBED VERTICALLY TO A HIGH HOVER AND THE PILOT LOST CONTROL. THE PILOT STATED THAT HE HAD NOT RELEASED THE CYCLIC FRICTION BEFORE BECOMING AIRBORNE. THE PILOT INDICATED HE HAD ABOUT500 HOURS OF FLIGHT TIME BUT DID NOT SPECIFY THE TYPE AND NO SUBSTANTIATION OF THE TIME COULD BE MADE.

The National Transportation Safety Board determines the probable cause(s) of this accident as follows:

DIRECTIONAL CONTROL..NOT MAINTAINED..DUAL STUDENT JUDGMENT..POOR..DUAL STUDENT VERTICAL TAKEOFF..UNCONTROLLED..DUAL STUDENT INSTRUCTIONS,WRITTEN/VERBAL..DISREGARDED..DUAL STUDENT

Observations

The pilot apparently had some knowledge of the basic flight controls, but clearly did not have any experience. The sequence of events appears to go like this:

1. Pilot increases collective, helicopter is light on the skids
2. Increased torque causes nose right yaw, pilot correctly compensates with left pedal
3. Left translation. The pilot probably did not expect the lateral contribution of tail rotor thrust and/or cross winds and failed to compensate with right cyclic.
4. Greater lateral translation, more collective, helicopter lift off
5. Forward translation, pilot corrects with excessive aft cyclic
6. Pilot overcontrols with lateral cyclic causing excessive oscillation
7. Preoccupation with the cyclic probably caused pilot to ignore yaw control
8. Pilot adds more collective resulting a rapid vertical climb
9. Pilot fails to add sufficient left pedal to compensate for increased torque and increased clockwise yaw rate
10. Pilot reduces collective and attempts a descent
11. Reduced torque slows clockwise yaw rate
12. Pilot fails to control the descent with collective causing hard landing
13. Tail rotor contacts ground and shatters
14. Loss of anti-torque from tail rotor causes high speed clockwise yaw rate
15. Lack of stability results in dynamic rollover
16. Main rotor contacts ground
17. Camera man drops camera or considers fleeing the scene
18. Engine continues to run for a few more minutes
19. Camera man approches wreckage

The entire sequence is almost predictable. Even though the pilot had some idea of how helicopters operate, he was not prepared for several non-intuitive reactions:

• Increasing collective adds significant torque (right yaw)
• Translating tendency from tail rotor thrust
• Sensitivity of cyclic control

It can be boiled down to two challenges in helicopter pilotage:

1. Helicopter flight controls are highly interdependent, i.e. adjusting one control requires adjustment of the others
2. Helicopters are second order systems, e.g. forward cyclic causes forward acceleration rather than constant velocity

The former can be expected but the amount of correction requires many hours of training. The latter is by far the greater challenge. Very few people have experience with a second order (double-integral) control system. These types of systems can be highly unstable, leading to oscillation as observed in the video. The controls seem to have no rational affect to an inexperienced pilot. Experienced pilots manage the instability after learning to anticipate and quickly react to attitude changes. Proper control reaction on one level is instinctive, this is developed during early training. After considerable training, a higher level of reasoned anticipation is developed.

Most pilots require several hours of dual instruction just to manage one control effectively. After 10 hours or so, most pilots can maintain controlled hover under good conditions. Most pilots at this level still have difficulty with vertical takeoff and landing. Typically, 20 hours or more dual instruction is necessary before solo operations are possible.

Zero order systems are relatively easy to control. A computer mouse is an example of a zero order system: mouse position is linearly proportional to mouse pointer position. First order systems are slight more challenging. Automobile steering is a first order system: minor course corrections are necessary to maintain a constant heading. First order systems are non-intuitive, but do not take long to master. Second order systems are the most challenging to control. Second order systems can result in oscillations not found in zero and first order systems. Humans are surprizingly adaptive and are capable of managing second order systems as long as the time contants are within human reaction time (tens of milliseconds or so).