NTSB Safety Recommendations A-08-25 through -29

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                   NTSB SAFETY RECOMMENDATION
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National Transportation Safety Board
Washington, DC 20594

June 9, 2008

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NTSB Safety Recommendations A-08-25 through -29

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The National Transportation Safety Board makes the following 
recommendations to the Federal Aviation Administration:

Revise Advisory Circular (AC)-27, "Certification of Normal 
Category Rotorcraft," and AC-29, "Certification of Transport 
Category Rotorcraft," to include long-term durability 
testing of adhesive bond joints for helicopter blades to 
ensure safe operation throughout their design life in all 
environments and operating load spectrums that the blades 
will experience and to set service life limits accordingly. 
(A-08-25)

Require Robinson Helicopter Corporation to develop a 
nondestructive inspection technique or combination of 
techniques capable of consistently detecting bonding 
defects, such as voids, debonds, and weak (kissing) bonds, 
in bond areas between the skin and spar at the tip of the 
blade and between the skin and tip cap for R22 and R44 model 
helicopters. (A-08-26)

Require that all Robinson Helicopter Corporation main rotor 
blades be inspected using the effective and reliable 
nondestructive inspection method(s) developed in response to 
Safety Recommendation A-08-26 at intervals appropriately 
less than 596 hours time in service (TIS), which 
investigations have shown to be the earliest known TIS at 
which debonding occurs, to evaluate the bond joints between 
the skin and spar at the tip of the main rotor blade and 
between the skin and tip cap to find bonding defects. (A-08-
27)

Amend Airworthiness Directive 2007-26-12 and add 
requirements that the main rotor blades are to be inspected 
for crack(s) in the paint layer at the skin-to-spar 
bondline. Main rotor blades that contain a crack in the 
paint layer at the skin-to-spar bondline should be removed 
from service. (A-08-28)

Review the manufacturing processes and continued 
airworthiness requirements for blades manufactured by 
companies other than Robinson Helicopter Corporation, and, 
for those using adhesive bonding, determine if sufficient 
durability testing and inspections of adhesive bonds are in 
place to ensure the safe operation of the blades without 
failure throughout their designed life expectancy in all 
environmental and operating load spectrums that the blades 
will experience. (A-08-29)

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http://www.ntsb.gov/recs/letters/2008/A08_25_29.pdf

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The complete recommendation letter is available on the Web 
at the URL indicated above.

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Electronic versions of letters may or may not include 
enclosures; however, related publications, accident 
briefs, and aviation accident synopses may be found 
on the NTSB website.

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