http://www.aopa.org/gta/ad/main/inde...tail&Awcid=563
Here's the text of the Airworthiness Concern Sheet:
FAA Description of Airworthiness Concern
The Cessna Multi-Engine Service Letter ME78-2, dated February 13, 1978, and Airworthiness Directive (AD) 78-09-05 require a dye penetrant inspection of the rear spar cap. Dye penetrant is no longer considered acceptable for the following reasons:
(1) Neither the AD nor the Cessna Service Bulletin specifies which kind of penetrant is to be used in the inspection. Penetrant is available in
visible dye and fluorescent types along with many levels of sensitivity. So, there is variation in inspection results depending on which
combination of penetrant options used. Also, evidence shows that following up a visible dye penetrant inspection with a fluorescent
penetrant inspection can lead to reduced sensitivity in the fluorescent penetrant due to the potential mixing of the two penetrants. The reduced sensitivity makes detection of smaller cracks unlikely. See SID 57-30-02, Section 2-13-01, for clearer explanation.
(2) Cleaning the area appropriately without removing the tank is a concern since the access to the area is inadequate for proper pre- and post-cleaning.
(3) The use of penetrant materials in areas that have mating surface can create contamination for future processing; such as, painting and corrosion protective compounds. Inappropriate use of water washable penetrant materials can attract moisture that may cause corrosion.
(4) The only way to apply developer to this area is using dry or non-aqueous methods. Because of limited access, post-cleaning will cause the area to hold moisture that may cause corrosion.
(5) The eddy current equipment is already in use to do the bolthole inspections on the front spar, so cost increase should be minimal. There should be little or no clean up required of the rear spar, so no paint removal and repainting. The inspection is much quicker using eddy current.
The FAA is also considering eliminating Section II of AD 78-09-05 that states: “Airplanes found to have cracked spar caps, webs or web doublers during inspections required by the AD may be flown in accordance with FAR 21.197 to a base where the component replacement can be accomplished. When the spar cap is broken, the remaining structure will no longer meet residual strength requirements and further flight may not be safe.
At this time, the FAA has not made a determination on what type of corrective action (if any) should be taken. The resolution of this airworthiness concern could involve an Airworthiness Directive (AD) action or a Special Airworthiness Information Bulletin (SAIB), or the FAA could determine that no action is needed at this time. The initial Risk Assessment for this concern indicated that an AD or SAIB might be considered.