SBs and ADs: What’s the difference?

July 20, 2009

AOPA continues to receive calls from members that illustrate some confusion regarding service bulletins (SBs) and airworthiness directives (ADs). This was illustrated following the recent AD dealing with the potential for Cessna 150/152 rudder assemblies to jam. In a nutshell, SBs, service instructions, and mandatory service letters are issued by manufacturers, and compliance is not mandatory—except in the case of airplanes operated under FAR Part 135, or some aircraft under a progressive maintenance/inspection program. ADs are issued by the FAA, and compliance is required.

Another maintenance issue threatens to further confuse the pilot population. Precision Airmotive issued mandatory service bulletin MSA-13 on Jan. 30, 2008, which affects aircraft having Precision Airmotive/Facet/Marvel-Schebler Float Carburetors. Per MSA-13, the brass floats in those carburetors must be replaced with a new foam float. Lycoming’s mandatory service bulletin 582A essentially recommends the same change in all of its engines having the same carburetors.

On August 19, 2008, Kelly Aerospace issued Service Letter 027A, which states that engines having carburetors fitted with KAPS metal floats are not affected by the SBs mentioned above.

AOPA estimates that some 25,000 aircraft could be affected by these service notifications. Members with questions are urged to contact AOPA at 800/USA-AOPA (872-2672), or by e-mail.