Ramon Lopez/WASHINGTON DC Karen Walker/ATLANTADavid Learmount/LONDON

FOCUS ON WHAT caused the ValuJet Airlines McDonnell Douglas (MDC) DC-9-30 accident in Florida, USA, is concentrating on oxygen-canisters wreckage is slowly recovered from the Everglades swampland into which the aircraft dived on 11 May.

US National Transportation Safety Board (NTSB) attention is focusing on the fact that the DC-9 may have been carrying unauthorised flammable cargo, which it has linked with evidence of heat damage to the wreckage.

The discovery that oxygen-generator canisters were on board has diverted attention from earlier concerns over the effectiveness of the US Federal Aviation Adminstration's oversight of low-cost operators flying old aircraft.

NTSB vice-chairman Robert Francis says: "We are particularly interested in [fuselage and cabin] parts that we find have some indication of heat damage". The aircraft did not burn after impact because it was submerged in water.

ValuJet president Lewis Jordan protested on 16 May that information is too quickly being proclaimed as evidence, saying that the allegedly dangerous oxygen-generator canisters were in fact declared empty of chemicals on the aircraft's cargo manifest. The NTSB acknowledges that, by 17 May, it had still not found any of the suspect canisters.

If they were not empty and were activated, these can generate such intense heat and are classified hazardous materials. ValuJet is not authorised to carry materials, but Jordan insists that the evidence at present is that the canisters were empty and therefore legal cargo. He acknowledges that he can not say for certain that all the canisters were empty, but points out that, so far, no-one else can be certain.

ValuJet, however, insists that while it may not carry hazardous materials for commercial carriage, it is permitted to carry certain hazardous materials "...that are to do with the operation and maintenance of our airline". ValuJet operates McDonnell Douglas (MDC) MD-80s, which are fitted with the oxygen generators as standard in their passenger emergency-oxygen systems.

The NTSB and the FAA have ruled out engine failure and repaired wiring as the causes of the crash. NTSB vice-chairman Robert Francis says: "We are finding more pieces of aircraft with what we believe is soot on them - although we haven't yet confirmed it is soot."

The NTSB says that the flight-data recorder registered a sudden increase in interior air pressure before the aircraft crashed, indicating a possible explosion. It shows that power in the right Pratt & Whitney JT8D dropped sharply while the left maintained power.

Whether the accident could have a lasting affect on ValuJet's fortune is not clear. It will not be possible to establish the initial impact on load factors until the June traffic figures are available. After the accident, the share price plummeted by nearly one-quarter, but has since recovered.

ValuJet had previously suggested that its dramatic growth would begin to slow, and analysts began to raise concern over a recent tail-off in load factors, and the carrier's weak performance on its newer US East Coast routes. Jordan has said that the airline will make no decision on growth until the outcome of the investigation is known.

On 11 May, at about 14:30 local time, the 27-year-old DC-9 (N904VJ) left Miami International for Atlanta's Hartsfield International. Passing 10,500ft (3,200m) in the climb, the crew declared an emergency, reporting fire in the cockpit and cabin, and requesting return to Miami.

In the last exchange, the flightcrew asked for the closest airport and controllers directed them to Opa Locka Airport, but some 11min after the initial call, the aircraft dived steeply into a swamp some 22km (12nm) west of Miami airport, killing all five crew and 105 passengers aboard.

The DC-9-30 was operated by Delta Air Lines until 1992. After being stored for a year, it was overhauled by MDC and delivered to ValuJet. Between 1994 and 1996, the aircraft suffered several minor inflight mechanical malfunctions, causing the crew to return to the point of departure.

A US Transportation Department statement released on 15 May reveals that ValuJet, among ten low-cost new-entrant operators studied, "...dominates the accident data, with five accidents and three serious accidents in the carrier's relatively short history". None of these was fatal.

ValuJet had an accident rate of 4.228 per 100,000 departures, while the ten carriers had an accident rate of 0.335 accidents per 100,000 departures, compared with 0.298 for the eight biggest US operators. Former NTSB head Carl Vogt, however, says that the agency had been studying US carriers since deregulation in 1978 and had been unable to establish a direct link between low cost and safety.

MDC will continue development of the MD-95 regardless of whether ValuJet fulfils its launch order to take 50 aircraft. New Douglas Aircraft president Mike Sears says that he is is confident that ValuJet and his 100-seat-aircraft programme will survive. ValuJet is the only client for the MD-95.

Source: Flight International