Stuck pedal

September 14, 2009 by Tim McAdams

For a helicopter pilot, one of the more difficult anti-torque system failures to deal with is when the tail rotor thrust becomes fixed or limited to a certain amount. This could happen if something jams or blocks the pedals or the associated linkage.

In flight, the pilot needs to determine at what position the pedals became stuck. In a counterclockwise turning rotor the more power a pilot is using, the more left pedal input is required. In this case, the left pedal is often called the power pedal. Should something jam the pedals during a high power take off or at maximum cruise speed, the tail rotor will be producing a lot of thrust.

The following illustrates the challenges of performing this type of emergency landing. As the pilot slows the helicopter to attempt to land, the helicopter approaches its most efficient airspeed (normally about 60 knots). The pilot must reduce power to prevent the helicopter from climbing. This would normally require adding right pedal, but since this is not possible the nose will start to yaw left and if airspeed gets too slow the helicopter will start spinning. The only way to stop the left yaw or spin is to add power, but that makes the helicopter climb and that’s not good because the pilot needs to get close to ground to land.

Some instructors have different techniques to land with a stuck left pedal. One method is to approach the longest runway available at cruise speed. This keeps power high and the helicopter pretty much in trim. Since the nose is trying to turn left, the tail wants to move right so finding a runway with a right crosswind will help the vertical fin oppose the left turning motion. Once over the runway, slowly start to decelerate with aft cyclic. As the helicopter’s airspeed decreases the pilot will need to reduce power. Lowering the collective should be done as carefully as possible as the nose will begin to yaw left. As the airspeed continues to drop below 60 knots the airflow over the vertical fin will at some point no longer be able to prevent the helicopter from spinning. The good news is that as the helicopter continues slowing below 60 knots more power is needed. Timing is critical as the pilot needs to keep adding power to prevent the helicopter from spinning, but can’t add too much power or the helicopter will climb. If all goes well and the pilot is able to get the helicopter to a very low hover with little or no left spinning, he or she will have the best chance to put it on the ground without rolling over.

A stuck right pedal makes it a little easier to land because in this case the pilot needs to keep power low. A common low-power landing maneuver in a helicopter is called a running landing. Since hovering requires more power, the pilot would touchdown on a flat smooth surface (a runway for example) with forward speed allowing the helicopter to slide to a stop. It must be performed carefully and is a maneuver that student pilots practice.

Different helicopters and situations will require different procedures. For example, in a clockwise turning rotor the same concepts apply, however the yawing direction and pedal inputs are reversed, as the right pedal is the power pedal. When provided, the manufacture’s recommended procedure should be followed.

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11 Responses to “Stuck pedal”

  1. Avi Weiss Says:

    Tim;

    Though I may have read it wrong, sounds like you are describing a “quick stop” method, which I hadn’t really heard or tried before. I will go out and simulate and see how it works…

    -avi

  2. Ehud Gavron Says:

    Avi, I’m looking forward to learning from your experiment as well… if you can get a video of it that would be awesome!
    Ehud

  3. R Kirk Says:

    Am I misreading the last sentence in the 2nd paragraph? At max cruise, would not the tail rotor be producing very little thrust?

  4. P.Pier Says:

    R Kirk,
    I believe as you.,, @ max cruise the tail rotor is doing very little work,as the vertical stabilizer is working at a high
    efficiency to counter the yaw. It is only when you begin to reduce power that you need right pedal to maintain heading.
    To reiterate,,Only when you change power settings @ cruise speed do you need to adjust the pedals
    Of course this is my opinion ,,,,I could be wrong..ha.

  5. Ehud Gavron Says:

    I agree that in general there’s less work to be done on the pedals (anti-torque) at a high airspeed due to the vertical stabilizer. However, if you think about the number of times you notice the trim-strings aren’t vertical (or for those with a turn-coordinator we “step on the ball”) you’ll notice that in any crosswind we do have to crab. When we crab we’re using our anti-torque mechanism (I’m purposely not saying tail-rotor just to include all those NOTAR guys ;)

    So at max cruise we still need to maintain our heading while keeping the aircraft positioned with its nose to the wind. Now in zero-wind conditions or in “wind from 12 or 6 O’clock” conditions there’s no doubt the vertical stabilizer is doing its job — keeping us on course.

    Happy Flying,

    Ehud
    (no longer a student pilot ;)

  6. Chris Says:

    Does anybody remember the Enstrom caught by a news chopper doing a stuck pedal landing? He was yawed left on approach, and I thought he’d pull a little power to align with his ground track and then run it on, but he ended up going another 180 degrees or so at the termination of the approach and landing sideways. Any explanation? The video is here: is here.

  7. Bastian Says:

    Just a thought here.. but I was wondering how about slowing down and climbing simultaneously to keep power required high and then basically taking your sweet time descending in an OGE hover or very slow forward flight so that power required is high (naturally being very cautious not to get into VRS). What do you guys think?

  8. J-HO Says:

    No mention of reducing Rotor RPM ? I know the initial reduction will aggravate the left yaw, but the resulting INCREASED induced drag/ torque and DECREASED tail-rotor effectiveness would definitely be two resources I’d want to use in that situation.

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