Incident Overview

Date: Tuesday 16 May 1995
Aircraft Type: British Aerospace Nimrod R.1P
Owner/operator: Royal Air Force – RAF
Registration Number: XW666
Location: 7,2 km NE off Lossiemouth – ÿ United Kingdom
Phase of Flight: En route
Status: Destroyed, written off
Casualties: Fatalities: 0 / Occupants: 7
Component Affected: No 4 engine electrical loom.No 4 engine electrical loom.
Category: Accident
On a routine post-servicing airtest of a Nimrod reconnaissance variant, an aircraft experienced a catastrophic fire resulting in a controlled ditching into the Moray Firth. The fire originated from a faulty DC electrical loom connected to the No 4 engine, which triggered a cascade of events leading to the complete destruction of the aircraft. Initial observations revealed a fire on the starboard wing, with subsequent explosions causing panel damage and a loss of control. The captain initiated a controlled ditching, ultimately resulting in the aircraft sinking. The investigation revealed a mechanical failure within the DC electrical loom, exacerbated by an arcing event triggered by the anti-icing system activation. The failure of the turbine disk, coupled with a damaged bypass casing and fuel leak, initiated the fire’s rapid spread.On a routine post-servicing airtest of a Nimrod reconnaissance variant, an aircraft experienced a catastrophic fire resulting in a controlled ditching into the Moray Firth. The fire originated from a faulty DC electrical loom connected to the No 4 engine, which triggered a cascade of events leading to the complete destruction of the aircraft. Initial observations revealed a fire on the starboard wing, with subsequent explosions causing panel damage and a loss of control. The captain initiated a controlled ditching, ultimately resulting in the aircraft sinking. The investigation revealed a mechanical failure within the DC electrical loom, exacerbated by an arcing event triggered by the anti-icing system activation. The failure of the turbine disk, coupled with a damaged bypass casing and fuel leak, initiated the fire’s rapid spread.

Description

The aircraft was one of three Nimrod reconnaissance variants and had just undergone a major servicing at the Nimrod Major Servicing Unit (NMSU), RAF Kinloss by RAF maintenance personnel. Nimrod XW666 departed on a routine post-servicing airtest. After approximately 35 minutes of flight, following a test of the aircraft’s anti-icing system, the No 4 engine fire warning illuminated. Whilst the crew were carrying out the fire drill, the No 3 engine fire warning also illuminated. A rear crew member confirmed that the aircraft was on fire and advised the captain that panels were falling away from the starboard wing. After two explosions, the captain feared for the structural integrity of the aircraft and decided to ditch before he lost control authority. Without the aid of flaps, which failed to operate because of a fire/associated hydraulic failure, he completed a controlled ditching into the Moray Firth. The aircraft bounced twice onto the sea before settling. The fuselage broke into two and the aircraft subsequently sank. Parts were salvaged and the cockpit section is now on display at AeroVenture South Yorkshire Aircraft Museum in Doncaster. With the assistance of the Department of Transport’s Air Accident Investigation Branch, the Inquiry established that despite the correct application of maintenance procedures, the DC electrical loom attached to No 4 engine had sustained mechanical damage, although it could not be positively determined how or when. Arcing occurred when the engine anti-icing system was switched on and this led to initiation of the air starter system. With the No 4 engine already running at idle as part of the overall airtest there was no load on the starter turbine, which quickly ran up to high speed. The nut holding the turbine disk in place failed, allowing the disk to move back on its shaft and out of its protective housing. It then struck the engine bypass casing and the No 2 fuel tank, puncturing both. The resultant fuel leak was ignited either by electrical arcing within the faulty DC loom or by the heat of the engine. The fire spread rapidly to the wing area and forward to the engine intake area. The Inquiry concluded that a sequence of technical difficulties led to the uncontained fire.

Source of Information

http://www.skybrary.aero/index.php/NIM,_manoeuvring,_northern_North_Sea_UK,_1995, http://www.aeroventure.org.uk/xw666.phphttp://www.skybrary.aero/index.php/NIM,_manoeuvring,_northern_North_Sea_UK,_1995, http://www.aeroventure.org.uk/xw666.php

Primary Cause

Faulty DC electrical loom attached to the No 4 engine.Faulty DC electrical loom attached to the No 4 engine.

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