Graham Warwick/Atlanta
Propeller-blade failure is the suspected cause of the 21 August crash of an Atlantic Southeast Airlines (ASA) Embraer EMB-120 Brasilia near Carrollton, Georgia, USA, which killed the captain and four passengers. Evidence of a blade-spar fatigue-fracture has been found.
Blade failure has also been implicated in a 3 August incident involving a Luxair EMB-120 on approach to Luxembourg Airport. The aircraft landed safely even though the starboard propeller and gearbox completely separated from the aircraft, damaging the wing.
In March 1994, the US Federal Aviation Adminstration ordered inspections of Hamilton Standard blades following failures in Brazil, on an EMB-120, and in Canada, on an ATR 42. Both aircraft landed safely.
An ASA EMB-120 crashed at Brunswick, Georgia, on 5 April, 1994 - killing all 23 people on board - when a worn spline allowed the propeller control unit to reduce the blade pitch to below the flight-idle setting.
ASA Flight 529 was en route from Atlanta, Georgia, to Gulfport, Mississippi, with 26 passengers and three crew. Passengers report hearing a bang about 30min into the flight. A loud noise is heard on the cockpit voice recorder (CVR), according to the US National Transportation Safety Board.
The flight attendant reported to the pilot that the left propeller had stopped turning. According to the CVR, the crew began shutdown procedures but attempts to feather the propeller did not work. The aircraft became difficult to control and began to lose altitude.
Air-traffic control advised diversion to nearby West Georgia Regional Airport, but the aircraft came down some 9min later in a field 13km (7nm) from the airport.
The left Hamilton Standard 14RF four-blade propeller was found away from the main wreckage. One blade had only 300mm remaining attached to the hub. The outer part has not yet been recovered. Examination revealed that the blade spar had fractured under tension at a fatigue crack.
The blade had been returned to Hamilton Standard after the FAA-mandated inspection for cracks in the taper bore - the cavity which runs up the centre of the aluminium spar - uncovered an anomaly. The repaired blade had logged 2,400h operation since installation in August 1994.
It is not clear why the aircraft could not remain airborne on one engine. Two passengers report that the propeller appeared to have detached itself from the engine, exposing the drive shaft, and re-attached itself to the wing leading-edge outboard of the nacelle.
The flight-data recorder (FDR) shows left-engine torque suddenly reduced from 63% to 0% at 18,000ft (5,490m). The Pratt & Whitney Canada PW118 was still producing low power when the aircraft hit. Propeller pitch was found to be 10degrees short of full feather. The FDR shows the pilot made several turns and right-engine power changes in the descent.
Source: Flight International
