0
$\begingroup$

Air Moorea Flight 1121 crashed because its up-elevator cable broke, allowing the elevator to blow to its faired position and thus be unavailable to counteract the pitch-down moment caused by the flaps being retracted;1 the DHC-6 elevator control system has two cables (up-elevator and down-elevator, distinguished by what part of the aft-quadrant bellcrank they attach to), and, if one breaks, the tension in both is released and the elevator floats. No redundancy is provided in the form of a second or third set of elevator cables, unlike how most airliners have double- or even triple-redundant flight controls. Why does the DHC-6 have only a single set of elevator control cables, rather than two or three?

1: No matter that retracting one’s flaps should not do that.

Improve this question
$\endgroup$
3
$\begingroup$

The Twin Otter isn't certified in a category that requires duplicate control runs with split surfaces. It's more or less a single engine Otter with two PT-6s and a redesigned tail. Those requirements apply to heavier aircraft than the DHC-6.

Improve this answer
$\endgroup$
3
  • $\begingroup$ If it were a one-person general-aviation aircraft, I'd buy that explanation, but this is an airliner we're talking about here (albeit a small one). $\endgroup$
    – Vikki
    Mar 6 '19 at 3:44
  • $\begingroup$ The Beech 1900 is the Twin Otter's closest competitor in the commuter airline business, and it also has a single cable circuit. You don't see separate left and right elevator control systems with pitch disconnects until you are in the Transport Category airplanes of the Dash 8/ATR size. $\endgroup$
    – John K
    Mar 6 '19 at 4:40
  • $\begingroup$ @Sean doesn't matter. The requirements are based on aircraft size, weight, etc. and not so much the purpose it's used for. $\endgroup$
    – jwenting
    Mar 13 '19 at 4:50

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.