Sender: <marv@lancaironline.net> (Marvin Kaye)
To: lml
Date: Mon, 03 Jun 2002 19:15:26 -0400
Message-ID: <redirect-1281153@logan.com>
From: RWolf99@aol.com
Subject: Re: Non standard metal props on Lancair 320/360
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Concerning the fatal prop separation on N320L (the red factory 320) and Jim 
Frantz' comments on propeller suitability --

1)  Jim is absolutely right.  Much analysis and sometimes testing is done on 
engine and propeller combinations.  Personally, I would not fly behind an 
unapproved combination -- but some people call me a wimp.

2)  N320L may not have crashed due to an unacceptable propeller and engine 
combination.  The following are exerpts from the NTSB report on the crash.

"The propeller was not found in the engine crater nor recovered near the 
wreckage site. The crankshaft was sheared at the propeller flange. The 
crankshaft was retained for further testing <snip>  A farmer who lives near 
the accident site discovered the propeller located approximately 115 degrees 
at 3,000 feet from the accident site while harvesting his crops. Both 
propeller blades and hub assembly appeared undamaged with the crankshaft 
flange still attached to the hub."

Why did this happen?  More excerpts...

"The crankshaft flange was examined by the NTSB's Metallurgical Laboratory in 
Washington, D.C.. The NTSB metallurgist's factual report on the crankshaft 
flange stated "...examination of the propeller mounting flange showed that 
five of the six fracture areas between lightening holes contained evidence of 
fatigue cracking." Further examination of the fatigue cracking in the flange 
revealed no evidence of scratch marks, abusive machining damage, or other 
defects that may have contributed to the initiation of the cracking. The 
thickness of the propeller mounting flange was measured as 0.255 inches. A 
representative of Lycoming stated that the specified thickness of the 
propeller mounting flange on a P/N 74780 crankshaft is 0.26 inches to 0.28 
inches. Hardness measurements on the flange averaged 30.4 HRC, below the 
specified range of 32 HRC to 36 HRC. <snip> The propeller mounting flanges on 
the crankshaft from IO-320-B1A engines installed in Piper PA-30 airplanes are 
the subject of Airworthiness Directive (AD) 65-03-03 (referencing Lycoming 
Service Bulletin 300B). This AD requires visual or magnetic particle 
inspection of the propeller mounting flange before the next flight following 
certain aerobatic type maneuvers not approved for normal category aircraft. 
The compliance of this AD note is not required for experimental aircraft. The 
Pilot's Operating Handbook for the Lancair 320 allows for aerobatic 
maneuvers. "

Why did the airplane crash after the crankshaft sheared?  The report goes on 
to say that losing the mass of the prop pushed the CG well aft of the aft 
limit.

I'm not pointing fingers at Lancair here, although it seems like the NTSB was 
trying to suggest there was a defective part which might have been detected 
had the AD been complied with.  The point is that it's not clear that the 
320L crash was caused by a prop failure due to an unapproved prop/engine 
combination.  However, this sort of thing CAN happen with an unapproved 
engine/prop combination, which is the real lesson here.  A prop failure may 
result in worse than just gliding to the nearest corn field, so if you think 
your risk with an unapproved combination is limited to an unscheduled 
off-airport landing, think again.

Another lesson this teaches us, although off-the-topic, is a caution to pay 
attention to an AD even if compliance is not mandated by law.  You may choose 
to not comply, but make sure it's for a better reason than "I don't have to." 
 (And no, I'm not suggesting that Lancair did that.)

- Rob Wolf