The American Caliban (substitute) wrote,
The American Caliban

From today's edition of the RISKS digest: "Quirks" considered harmful.

(Syndication available on LJ as risks_digest)

I think "quirk" is even better than "glitch" for wrecking a $133 million aircraft and nearly killing the pilot. Next time my boss is mad because one of my infrastructure maintenance setups doesn't work I'll say I have a "quirk".

Date: Wed, 15 Jun 2005 11:10:34 +0200
From: "Peter B. Ladkin" <>
Subject: Details of F/A-22 crash December 2004

On 20 Dec 2004, an F/A-22 Raptor, the USAF's new air-superiority fighter, crashed 11 seconds after takeoff from Nellis AFB, Nevada. It is the first production aircraft to be lost. They are said to cost $133 million each. The results of the investigation from the USAF Accident Investigation Board (AIB) are reported in this week's Flight International (14-10 June, 2005, p9).

The pilot ejected with the aircraft near-inverted. The aircraft struck the end of the runway going backwards.

There are three rate-sensor assemblies (RSA), manufactured by BAE Systems in the flight control system (FCS). There is a known "quirk" in the RSA, which is "programmed so that it could interpret a momentary power loss [to the FCS] as an instruction to enter test mode, which freezes or "latches" the unit, according to the AIB report."

The pilot shut down the engines during a maintenance check pre-take-off, thinking the FCS was continuously powered by the auxiliary power unit (APU). The FCS in fact loses power briefly during a shutdown, and that appeared to suffice to latch all three RSAs. "The AIB attributed the pilot's mistake to "ambiguous" language in the aircraft's technical orders."

The manufacturer, Lockheed Martin, has returned about 20 RSAs to BAE Systems for suspected latching events. Before this crash, such events only affected one or two of the RSAs, not all three together. There is a pilot warning for partial RSA latching, but no warning if all three latch.

The RSA has been redesigned and is being installed on the fleet.

Peter B. Ladkin, University of Bielefeld, Germany
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