Protecting your tail

May 1, 2009 by Tim McAdams

Not visible from the cockpit, a helicopter’s tail rotor is perhaps the most vulnerable component to striking objects in a hover. EMS pilots are especially at risk, as their job involves routinely landing in obstacle rich environments.

In 2003, a Bell 430 was substantially damaged when its tail rotor hit a roadway sign during an off-airport landing at night. Prior to touchdown, the pilot said he rotated the aircraft and landed on an easterly heading, at which point the medical crew departed the helicopter. Then, the pilot decided to reposition the aircraft to face west for departure. During the hovering turn the tail rotor hit a steel reflector post. The aircraft touched down on the left rear skid first and came to rest 180 degrees from its initial heading. The tail rotor and gearbox assembly had come apart and departed the helicopter.

Darkness certainly makes objects harder to see. However, two years prior to this accident, during daylight conditions, a Bell 222UT was substantially damaged when its tail rotor hit a barrel while landing on a paved traffic turn-around area. The pilot said that while hovering, he decided to reorient the aircraft to help load the patient easier. During the right pedal turn, the tail rotor struck a 55-gallon trash barrel. The helicopter yawed to the right and the pilot brought the throttles to flight idle and landed the helicopter. The tail boom was twisted, the tail rotor blades were damaged, and the tail rotor gearbox was nearly separated from the airframe.

Although a tail rotor strike in a hover can cause serious damage, the potential for personal injury is low compared to what can happen in flight.

In 1999, a Bell OH-58A, on a photo flight with doors removed, was destroyed on impact with the terrain and the private pilot and passenger sustained fatal injuries. A witness reported that he saw the helicopter flying at an altitude of approximately 350 to 400 feet. He saw what was possibly a large bird hit the rear rotor of the helicopter. The helicopter made three to four rotations during its descent.

Examination of the tail assembly revealed an elastic material with navy blue yarns wrapped around the tail rotor. The material, along with a sample of a navy blue warm-up jacket found along the reported flight path, was sent to the NTSB’s Materials Laboratory for examination. The color, size, and texture of the navy-blue yarns in the elastic material were consistent with those found in the navy blue warm-up jacket. The NTSB concluded that the jacket exited the helicopter and became entangled in the tail rotor.

Removing a helicopter’s doors places the tail rotor at increased risk. In 1993, an R22 helicopter flying with its left door removed crashed after an aluminum kneeboard exited the helicopter and struck the tail rotor.

There have been numerous cases where objects have come out of the cabin or an unsecured baggage compartment and struck the tail rotor. In some cases the pilots have been able to enter autorotation or otherwise land with minor damage or injury. However, as with the two preceding accidents, the tail strike inflicted enough damage to cause the tail rotor assembly to come apart. In these cases, the resulting center of gravity shift will make recovery nearly impossible. The importance of protecting the tail rotor cannot be emphasized enough.

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5 Responses to “Protecting your tail”

  1. CW4 Ken Biddulph Says:

    In the UH-60L Blackhawk (US ARMY) we are fortunate that we have a crew chief to clear our tail before we turn. However, of those that choose to turn before the crewchief clears the tail, a few have learned the hard way that obstacles don’t move just because the pilot decides to turn.
    We have at times flown with the doors off when we are in Iraq. This helps with visibility when landing in a dust cloud using night vision goggles. However, in my battalion, we were required to teather all our “loose items” with a lanyard of some kind before flight. This actually saved my checklist (the size of a small novel) from leaving the aircraft and going back by the tail rotor. The crew chief grabbed the checklist outside the aircraft (through his window), cut the lanyard, and brought the checklist back in. The checklist was a bit blown apart, but it was still good enough to continue using and the helicopter sustained no damage.
    Take care, Ken

  2. Phillip Peterson Says:

    This story affirms that aircraft don’t crash – pilots crash!

  3. Avi Weiss Says:

    This is where the NOTAR and Fenestron designs really earn their keep.

    While the above systems do have some additional mechanical complexities, and in some cases pilots have reported control “lag” or “spongy-ness”, The additional maintenance and slight pilots adaptation to the system is well worth the increase in safety margin by greatly reducing the probability of loss of yaw control due to inadvertent obstacle contact with the tail.

    Of course, if the tail is swung hard/fast enough, the thrust producing mechanism itself may be momentarily protected, but the energy absorbed by the tail structure on impact may be enough to cause wholesale structural damage, which will cause yaw control loss ANYWAY.

    So as always, look carefully, and turn slowly, ESPECIALLY when off-field.

    -avi

  4. Kevin LaCroix Says:

    why not tail-mounted cameras coupled with the gyro with a dash display that displays from the camera in the direction of movement. Then the pilot(s) could see the obstacles in advance….

  5. Duane Zentgraf Says:

    Good story, keep them coming

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