SAIB ACE-99-05 —

No. ACE-99-05 November 17, 1998

Published by: FAA, AFS-610, P.O. Box 26460, Oklahoma City, OK 73125 This is issued for informational purposes only and any recommendation for corrective action is not mandatory.

Introduction: The purpose of this Special Airworthiness Information Bulletin (SAIB) is to advise registered owners of certain Cessna twin engine models of the need to determine if there is adequate alternate crankcase breather provisions.

This SAIB is being sent to registered owners of: Cessna 300 and 400 Series Model airplanes except for the 303, 336 and 337 series airplanes.

Background: The Federal Aviation Administration (FAA) has received service difficulty reports concerning oil loss on certain Cessna twin engine airplanes. This oil loss was due to the forward crankcase oil seal being dislodged by abnormally high crankcase breather pressure. The abnormally high crankcase breather pressure was caused by icing of the crankcase breather vents. These airplanes either did not have, or had inadequate alternate crankcase venting provisions which are intended to ventilate the crankcase in the case of the icing of the primary vent. This condition may have occurred due to inadequacies in the original design or the unintentional deletion of the alternate venting provisions by field repair and/or modification. The original venting provisions were in many cases the installation of a hose section in the breather line that had a elongated hole in it.

Even though Cessna has released service information concerning this problem, the FAA has not concurred with the Cessna provisions as alleviating the condition.

The FAA has not mandated this modification but is strongly recommending that owners/operators of the affected airplanes examine the crankcase venting provisions installed on their airplanes for the existence of adequate alternate venting provisions, which should be a slit or hole (at least approximately one inch by .25 inches) in the breather line within a minimum of six inches inside the cowling.

If these provisions do not exist, is it recommended that alternate crankcase venting provisions be incorporated per the below figure.

NOTE: The FAA is considering several options, including rulemaking action, to mandate these recommendations.

2 ACE-99-05

Drill 5/16” and elongate as shown lengthwise only Diameter of hose 3 inches Breather vent tube Air flow Cowl skin, (reference) AN737 hose clamps or equivalent 6 to 9 inches Breather outlet (reference) 1 ½” 3/8” typical

For Further Information Contact: Federal Aviation Administration, Wichita Aircraft Certification Office, Attention: Mr. Paul Pendleton, 1801 Airport Road, Mid-Continent Airport, Wichita, KS 67209; or, Federal Aviation Administration, Project Support Office, ACE-112, Attn: Mr. Karl Schletzbaum, 1201 Walnut; Suite 900, Kansas City, Missouri 64106, telephone (816) 426-6932, fax (816) 426-2169.