Jet crew averted Dublin air disaster

THE crew of a jumbo jet averted disaster in the skies over Dublin when they managed to land the aircraft without knowing how fast it was going or how high it was flying.

The Boeing 747 cargo plane operated by United Parcel Service caused a full-scale emergency at Dublin Airport when key instruments failed after a pre-flight checking error by maintenance staff.

At one point as the flight commander turned the stricken plane for home, he had three different speed readings ranging from 170 knots to 300 knots and did not know which, if any, was correct.

He also, according to the resulting inquiry by the Department of Transport's Air Accident Investigation Unit, "had no idea of his true altitude except that he was staying on top of the clouds".

To compound the 39-minute crisis, the crew's preferred option of re-routing to Shannon where there was a longer runway was ruled out because of bad weather.

Investigators said the performance of the commander and his seven crew members was excellent and was the key factor in bringing the plane home safely in what they said was a "potentially disastrous situation".

They said the crew and aeroplane were also saved by the fact that they were on a test flight which was routine following maintenance and such flights were only conducted during daylight.

The incident happened in May 2000 but the report has only just been published. The AAIU said its investigation was hampered by confusion among staff about a parallel investigation by the Irish Aviation Authority.

The AAIU's function is to investigate incidents with a view to making safety recommendations without apportioning blame while the IAA has the power to prosecute and sanction personnel and formally cautions them prior to beginning an inquiry.

"It is therefore possible that the staff experience of being formally cautioned during the course of an IAA investigation may have had a detrimental effect on the willingness of staff to assist the AAIU investigation of this occurrence," the report states.

Investigators found that staff with Team FLS, an aircraft maintenance contractor at Dublin Airport, had left open the drainage caps on air pressure ports on the aeroplane, believing that the next shift taking over would complete the maintenance programme and pre-flight check. The next shift in thought the job was complete.

The ports measure air pressure while the plane is stationery and moving, the difference between the two giving the airspeed. Left open, the static drainage ports gave an incorrect reading resulting in a falsely low airspeed.