Mount Gambier T-VASIS ERSA caution
Some may recall the RFDS Super Kingair crash at Mount Gambier during a night approach to runway 18 in low cloud, mist and light rain. Date December 2001. The pilot was killed but the nurse aboard escaped minor injuries. The aircraft caught fire and was destroyed. The crash site was 3.1 miles short of the runway close to the extended centreline.
The ATSB report stated that the T-VASIS was operational and serviceable. ATSB were unable to find a cause of the accident although they hinted that perhaps the pilot flew below the DME (GPS) steps and crashed while not visual. One witness (not mentioned in the ATSB report) stated that he saw the landing lights of the aircraft shortly before it crashed.
There was no mention in the ATSB report of the possibility of erroneous T-VASIS glide slope indications although AIP AD 1.1-30 paragraph 5.1.1 Note 2 warns of the possibility of erroneous glide slope indications with any T-VASIS where weather consists of thin layers of ground fog or mist.
The BASIS Aviation Safety Digest (114/1982) revealed an incident at Perth where an RPT aircraft followed an erroneous T-VASIS fly-down signal while at the same time the ILS showed the aircraft low on the electronic glide slope. The pilot recovered in time but stated that the T-VASIS continued to provide false fly down presentation throughout. The T-VASIS was flight tested the next day and found to be operating correctly. BASIS stated in the article that the limitation of T-VASIS is that they are likely to produce erroneous indications in fog or mist and the systems cannot necessarily be relied upon in these conditions.
Fog and mist was present in both night approaches into Perth in 1982 and Mount Gambier in 2001.
Erroneous indications is an understatement. If not immediately recognised at night they can be deadly.
The latest ERSA (November 2003) now has the first acknowledgement that an erroneous T-VASIS indication may have occurred. It reads as follows: For Mount Gambier...Note 2..CAUTION: RWY 18/36 AT-VASIS susceptible to erroneous fly-up or fly-down signals under certain weather conditions.
It may go some way towards explaining why a highly experienced RFDS pilot with hundreds of black hole night approaches to his credit, would inexplicably fly wings level into the deck 3 miles on final approach. It was his first and last night landing into Mount Gambier.