Board calls for action after Garuda crash-landing probe
Pilots of turbofan-powered aircraft need better advice about operating their engines when descending through storms, says the US National Transportation Safety Board (NTSB) reporting on a total power failure on a Garuda Indonesia Airlines Boeing 737-300.
The NTSB is urging the US Federal Aviation Administration to re-examine “certification standards concerning rain and hail ingestion” by turbofan engines.
The accident that prompted the NTSB’s call happened on 16 January 2002 in Java, Indonesia. The 737 suffered flameout of both its CFM International CFM56-3B1 engines as it descended through storm clouds, even though the crew tried to avoid the “red” cells in the cloud centres.
Attempts to restart the engines failed, and the crew elected to ditch in the Bengawan Solo river. One flight attendant among the 60 people on board was killed, but 12 passengers were severely injured.
The NTSB points out two other instances of total power loss in 737-300s descending through storms with their engines at idle. One was an Air Europe 737-300 approaching Thessaloniki, Greece, on 21 August 1987, but in that case the crew managed to restart the engines and land safely. The other was a TACA 737 near New Orleans, USA, in which restart attempts failed and the crew made a successful emergency landing.
The NTSB deemed the probable cause in the latter incident to be flameout caused by water and hail ingestion. The common factor in all three cases was that the engines were at idle, and the aircraft was passing though storm clouds with heavy precipitation.
Following the TACA accident, the FAA issued an airworthiness directive that required operators descending though storms to keep a minimum engine fan speed (N1) of at least 40%, then later raised this to 45%. Flight idle is about 32% N1.
But by mid-1991, CFMI had incorporated modifications accepted by the FAA that allowed passage through storms with flight idle set. The NTSB says the Garuda 737’s engines had been appropriately modified.
The board says the FAA has begun a review of turbofan certification standards with this weakness in mind, and urges it to revise standards in the light of the recent additional evidence.
DAVID LEARMOUNT/LONDON
Source: Flight International
