Rain-soaked router can cause avionics bay short circuit

Urgent action is needed to prevent potentially catastrophic fires on Bombardier CRJ200s, the US National Transportation Safety Board (NTSB) has told the Federal Aviation Administration. The recommendation follows seven CRJ200 avionics bay fires – six of them in the last six months.

In all cases the crews landed safely, but in four the pilots lost their electronic flight instrument systems (EFIS). “The potential exists for an uncontained fire to compromise the oxygen line, which could develop into an even more critical situation,” says the NTSB, which has issued seven recommendations to the FAA.

The problem centres on the latest version of a contactor – a switching device to route power from the engine-driven generators – which is prone to moisture-induced short-circuits when rain gets into the avionics bay through an open cabin door.

The devices involved are versions of Tyco Hartman 1K4XD contactors with Ultem 2200 (polyetherimide) terminal bases.

The NTSB is calling on the FAA to immediately require:

  • operators to provide separation of electrical power sources to prevent potential EFIS loss in the event of contactor failure;
  • Bombardier to develop a means of protecting the affected contactors from moisture-induced short-circuiting, to be installed as soon as possible;
  • Bombardier to replace existing contactors.

Bombardier says the recommendations affect half of the CRJ100/200 fleet, and that in December it issued advice on a wiring modification to ensure electrical source separation, preventing EFIS failure.

In an unrelated incident, a Pinnacle Airlines CRJ440LR on 19 March suffered a windshield de-icer mechanism fire after take-off from Asheville, North Carolina, causing the crew to declare an emergency. The aircraft, carrying 30 passengers and three crew, returned to the airport and landed safely.

An independent study by Washington DC-based Safety Operating Systems (SOS) claims on-board fires are the industry’s “next major challenge”. SOS president Capt John Cox says in the USA one aircraft a day diverts because of cockpit or cabin smoke.

DAVID LEARMOUNT / LONDON

Source: Flight International

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