European safety regulators are examining whether modifications are required to terrain databases underpinning enhanced ground proximity warning systems (EGPWS) following the fatal loss of a Sikorsky S-92 helicopter on Ireland’s west coast.
The search and rescue-configured rotorcraft broke apart after striking 300ft-high cliffs on Black Rock island with the loss of all four crew members on board.
An initial report from the Irish Air Accident Investigation Unit (AAIU) disclosed that the S-92’s Honeywell-supplied EGPWS did not issue an alert as the helicopter approached terrain at night and in poor visibility.
However, the AAIU notes that crucial terrain features were absent from the fully certificated system. It says: “In relation to Black Rock and its lighthouse, the EGPWS manufacturer informed the investigation that ‘The lighthouse obstacle is not in the obstacle database and the terrain of the island is not in our terrain database.’
“The investigation is continuing to engage with Honeywell and other parties/agencies to reach a full understanding of this issue.”
The lighthouse is 50ft (15m) high and has an elevation of 282ft, says the AAIU.
Although declining to comment on the specifics of the Black Rock accident, the European Aviation Safety Agency says it is scrutinising the broader use of EGPWS devices in helicopter operations.
“The agency [EASA] is looking into this subject to identify needs for corrective actions or room for improvements, notwithstanding that, according to the flight manual of S-92, ‘navigation must not be predicated upon the use of [EGPWS] information’,” it says.
It adds that in order to be included in a terrain database, obstacles must have a minimum height of 30m.
An added difficultly is that helicopter-specific terrain-warning systems have been adapted from technology originally designed for operation by fixed-wing aircraft, whose requirements – and operational minima - are markedly different.
Although it believes the current systems are adequate, EASA says it is talking to the rotorcraft industry and national civil aviation regulators “to assess [the] future feasibility of any improved features”, subject to validation.
The CHC-operated S-92 (EI-ICR) was lost during the course of a SAR mission at 00:46 on 14 March. Its crew was flying an approach to Blacksod lighthouse, 9.7nm (18km) to the east of Blackrock, at 200ft and 75kt (139km/h) when the accident occurred.
Cockpit-voice recordings for the final seconds of the flight indicate that the aircraft commander had attempted to take evasive action at the last moment, pitching the helicopter sharply up, before it impacted cliffs at the western end of Black Rock island and broke apart.
The AAIU report says the recording “contains no reference by the crew to the presence of a lighthouse or terrain at Black Rock during their briefing for [Blacksod South approach]”, despite their inclusion in the operator’s route guide.