Metroliners subject of CAA attention in past

The charred right wing of the Airworks Metroliner. Wreckage was strewn for kilometres near Stratford in Taranaki. Picture / Amos Chapple

Metroliner aircraft similar to that which crashed in Taranaki on Tuesday night have been the subject of several Civil Aviation Authority airworthiness directives, some relating to potential fire risk.

All operators flying Metroliner SA226s were given directives in November 2001 and December 2003 in a bid to prevent the kind of mid-air fire implicated in the crash.

One directive involved wiring which passed through the fuel tanks, others involved problems that could cause a fire to break out in the plane's wheel well shortly after take-off and burn through the wing.

The Airworks Metroliner, carrying courier cargo from Auckland to Blenheim, crashed about 10.15pm on Tuesday, 5km east of Stratford.

The crash killed Clive Rodger Adamson, 43, of Wellington, and Anthony Brian Arthur Drummond, 41, of Manukau City.

Transport Accident Investigation Commission (Taic) investigator John Goddard told National Radio there had "certainly been an in-flight fire".

"Exactly at what stage of the whole sequence that happened I don't know at this point," he said.

Early indications were that the courier packages being carried were not the cause of the fire.

"A preliminary look at it suggests the fire has been external to the cargo hold," he said.

One airworthiness directive posted on the CAA website was specifically aimed at wheel well fire protection.

It said "drag" in the brake assembly could cause the brakes to overheat and, if the wheels were retracted as normal, damage hydraulic or fuel lines and feed a fire.

For all SA226 series Metroliners, operators were asked to replace the rubber fuel hose with a metal device, and to install only a specific brake shuttle valve.

The 2003 directive was aimed at preventing electric wiring in the fuel tanks from sparking inside the tank.

Operators were required to "detect and correct" chafing of boost pump wiring insulation in the fuel tanks, "and possible arcing that could provide an ignition source inside the fuel tank and consequent fire/explosion".

In addition to replacing chafed or bare wires, they were required to install special tubing around the pump wiring harness.

CAA warned its international counterparts in 2000 damaged wiring which could lead to "fire and explosions" had been detected in six of 20 Fairchild Metroliner aircraft in New Zealand.

The planes, operated by several airlines, had chafed fuel boost pump wiring.

The directive, which did not ground any planes, required inspection for chafed fuel boost pump wiring and repair or replacement, if necessary.

Similar faulty wiring igniting a fuel tank is believed to be the most likely cause of the explosion that destroyed the Boeing 747, TWA flight 800 off Long Island on July 17, 1996.

It exploded 14 minutes after takeoff from Kennedy International Airport in New York, killing all 230 people on board.

In September 2000 the CAA said there was enough concern to warrant immediate attention but "not so much as to require instant attention".

"We are not saying get out of the air before you blow up or anything like that," a spokesman said at the time.

"It is just a question of these wires being found which, in the worst case scenario it would cause a fire so get them on the ground and fix them."

The directive said that evidence of chafing to either the inboard or outboard boost pump wiring had been found.

"In one case there was evidence of arcing between the chafed wiring and the fuel check valve located immediately above the pump."

It warned that for the initial inspection it was advised not to use the fuel boost pumps to transfer fuel from the tank that was to be inspected.

Aircraft operators were told the directive addressed "a serious unsafe condition and should be actioned immediately".

Air New Zealand reported the wiring defects to the authority after it found the problem in five of its 12 Metroliners, then run as Air New Zealand Link.

Last year, US regulators said they would order modifications on 3800 commercial jets to further reduce chances of a fuel tank explosion like the one that destroyed TWA Flight 800.

The Federal Aviation Administration (FAA) wants the industry to install a fuel tank safety device on Airbus and Boeing aircraft to reduce the threat of combustion by neutralising potentially volatile fuel-air mixtures in empty or emptying tanks. This is achieved by replacing oxygen with nitrogen-enriched air.

- NZPA