Graham Warwick/ATLANTA
AIRLINES ARE inspecting Hamilton Standard propellers on several regional-turboprop types after the 21 August fatal crash of an Atlantic Southeast Airlines (ASA) Embraer EMB-120 Brasilia following blade failure (Flight International, 30 August-5 September, P12).
On 25 August, the US Federal Aviation Administration ordered the removal from service of all EMB-120 blades inspected and repaired under a previous airworthiness directive (AD). About 20 14RF-9 blades were affected, Hamilton Standard says.
At the same time, the FAA ordered that all 14RF- and 14SF-series blades inspected and repaired under the earlier AD be re-inspected. This affected some 350 blades on several aircraft types, including the ATR 42/72, CASA/IPTN CN-235, de Havilland Dash 8 and Saab 340.
On 28 August, the FAA ordered all EMB-120 operators to re-inspect the blades within 50 flights and every 1,250 flights thereafter. Some 2,800 blades are affected, says the manufacturer. The same inspection interval has been imposed on operators of other types using 14RF/SF-series blades - except those shot-peened to increase fatigue resistance. Some 6,000-7,000 blades are affected, Hamilton Standard estimates. The ultrasonic inspections are conducted on wing and take about 15min per blade.
The FAA also required Embraer and Hamilton Standard to conduct additional vibration and loads testing to re-establish the integrity of the EMB-120 propeller installation.
The fatigue fracture of the ASA blade was similar to two failures in March 1994, when an Inter-Canadian ATR 42-300 and a Nordeste Airlines EMB-120 lost parts of propeller blades in flight, but different to the in-flight failure of a blade on a Luxair EMB-120 earlier in August.
In the ASA and two previous incidents, failure was traced to fatigue cracking emanating from corrosion pits on the surface of the taper bore - a hollow cavity in the centre of the blade spar. In the Luxair accident, fatigue failure was initiated by damage to the surface of the spar, caused during manufacture or by improper handling of the propeller.
Source: Flight International
