[SystemSafety] Osprey [was: SKODA Crash in the UK - Cruise Control Stuck On]

[Peter Bernard Ladkin]

On 2016-11-26 20:11 , Mike Ellims wrote:

> 2.       Start/stop button has to be held – this was noted as being an issue in the crash with the
> Osprey tilt rotor reset button – the pilot never held the button in.

There is no indication of that in the material I reviewed in 2000. The pilots should have activated
the PFCS "reset" button, did so many times, indeed as many times as indicated, and each of those
times the activation had an effect. The problem is that these effects were deleterious to control of
the flight.

The findings from the Marines are in http://catless.ncl.ac.uk/Risks/21.33.html#subj1.1 . A causal
analysis is in http://catless.ncl.ac.uk/Risks/21.38.html#subj1.1 . And then I talked to Gene Covert,
an MIT helo expert who was on the Blue Ribbon Panel which investigated the accident at the request
of the SoD, and a postscript is at http://catless.ncl.ac.uk/Risks/21.41.html#subj7.1

Here is what I said in the second of those articles, the causal analysis:

[begin quote]

First, a brief review of what the JAG determined happened in the December
crash. A hydraulic line ruptured in the left nacelle. This line was part of
the primary flight control system hydraulics and activates the swashplate
actuators. There are three such systems, in a partially redundant
configuration. At the rupture point, the line was common to Systems 1 and 3;
System 1 was fully disabled, System 3 was isolated in the left nacelle, but
continued to function in the right nacelle, System 2 worked left and right.

This event caused the nacelle transition to stop, and the PFCS reset button
to illuminate in the cockpit. The aircrew pressed the reset button, as per
procedure. The PFCS computer software then caused "rapid" pitch and thrust
changes to be commanded and actuated. The rotors responded differentially in
time, because the physical actuation authority in each nacelle was
different: the right nacelle had two working hydraulic systems, and the left
nacelle only one. The aircrew pressed the reset button "as many as eight to
10 times [sic]" (JAGB) during the last 20 seconds of flight. The response
asymmetry and resulting flight behavior of the aircraft was directly
responsible for loss of control (LOC) of the aircraft and the aircraft
impacted the ground in a LOC condition.

[end quote]

PBL

Prof. Peter Bernard Ladkin, Bielefeld, Germany
MoreInCommon
Je suis Charlie
Tel+msg +49 (0)521 880 7319  www.rvs-bi.de





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