Boeing B75N1 equipped with Hartzell model 11C1 propeller blades - Civil Aviation Safety Alerts (CASA) No. 2016-06
Owners, operators and maintainers of Boeing Stearman model 75 aeroplanes
|Issuing Office:||Continuing Airworthiness|
|File Classification No.:||Z 5000-35|
|Document No.:||CASA 2016-06|
Transport Canada Civil Aviation (TCCA) has identified a potential hazard associated with the propellers used on some models of this aeroplane. The purpose of this Civil Aviation Safety Alert (CASA) is to provide some background information and recommendations for this problem.
On 10 September 2013, one of two blades on the propeller of a Boeing model B75N1 aeroplane experienced catastrophic failure during takeoff and initial climb. The failure of the propeller blade led to a severe vibration which broke the Continental W670 engine from the engine mounts causing the engine to fall off in flight. The aeroplane pitched up and became uncontrollable. The aeroplane struck the runway in a nose down attitude and both occupants sustained serious injuries. The pilot of the aeroplane reported that there were no unusual vibrations during the takeoff roll.
The Boeing model 75 was manufactured in several versions; some of these versions were certified to be operated with more than one propeller type. The Type Certificate Data Sheet (TCDS) contains information about the different versions of the aeroplane and the engines, propellers and other aspects of configuration that have been approved by the certification authority, the US Federal Aviation Administration (FAA). The TCDS number is A-743; it is available from the FAA Regulatory and Guidance Library (RGL) website.
In 1950, the FAA issued Airworthiness Directive (AD) 50-12-01. The official current version of the AD is available from the FAA website. This AD applies to all aeroplanes equipped with applicable Continental engines and Hamilton Standard ground adjustable propellers having blades, model 11C1 (Navy 4350, 4350F, 4350F1). As noted in the TCDS, the model A75N1, B75N1 and D75N1 of the Boeing Stearman Kaydet were produced with the Continental engine, and that engine is compatible with the Hamilton Standard blades 11C1.
The aeroplane that experienced the propeller failure was equipped with propeller blades model 4350F1. The part number was marked on the blades as 4350F-1. It was reported that the requirements of FAA AD 50-12-01 had not been embodied on the aeroplane. Examination by the Transportation Safety Board of Canada of the propeller after the accident noted the following:
- The blade retention clamp for the non-failed blade was likely to have had a pre-impact torque value lower than the recommended torque.
- No signs of pre-existing material defects were noted.
- The inspection of the fractured blade highlighted evidence of fast crack propagation.
- The crack initiation appears to have been caused by a general stress state rather than by a pre-existing defect. The origin of this failure may have resulted from prior stress history of the propeller.
Even if your aeroplane has been marked, placarded and operated in accordance with FAA AD 50-12-01, it is possible that the propeller blades have accumulated fatigue damage that increases the risk of failure. This damage may have accumulated when the propeller was operated at speeds above 1,900 RPM, which is the limit imposed by FAA AD 50-12-01. The AD permits operation above 1,900 RPM during takeoff, however there is no method or requirement to track the amount of time that the propeller has been operated in this range.
TCCA recommends operators to positively understand their propeller usage and history and if doubtful or no data is available, consider installing another approved propeller. TCCA reminds operators that there are other models of propeller that are approved for use with model A75N1, B75N1 and D75N1 aeroplanes. These other propeller models are listed on the TCDS.
For more information concerning this issue, contact a Transport Canada Centre; or contact Ross McGowan, Continuing Airworthiness in Ottawa, by telephone at 1-888-663-3639, by fax at 613-996-9178, or by e-mail at
ORIGINAL SIGNED BY
THE TRANSPORT CANADA CIVIL AVIATION SAFETY ALERT (CASA) IS USED TO CONVEY IMPORTANT SAFETY INFORMATION AND CONTAINS RECOMMENDED ACTION ITEMS. THE CASA STRIVES TO ASSIST THE AVIATION INDUSTRY'S EFFORTS TO PROVIDE A SERVICE WITH THE HIGHEST POSSIBLE DEGREE OF SAFETY. THE INFORMATION CONTAINED HEREIN IS OFTEN CRITICAL AND MUST BE CONVEYED TO THE APPROPRIATE OFFICE IN A TIMELY MANNER. THE CASA MAY BE CHANGED OR AMENDED SHOULD NEW INFORMATION BECOME AVAILABLE.