Aircraft
Certification Service Washington, DC U.S. Department of Transportation Federal Aviation Administration
AIR-22-10
April 29, 2022
This is information only. Recommendations
aren’t mandatory.
Introduction
This Special Airworthiness Information Bulletin (SAIB) informs pilots,
owners, operators, and maintenance personnel of turbofan-powered
airplanes produced by Textron Aviation Inc. (Textron) (previously
Cessna Aircraft Company, Beechcraft Corporation, Hawker Beechcraft
Corporation, Raytheon Aircraft Company, British Aerospace, Hawker
Siddeley) of the hazards associated with the engine cowl system. The
engine cowl system consists of engine nacelle cowl doors, and inlet,
exhaust, and thrust reverser components. Some components use
quarter-turn fasteners (often referred to by brand names such as
Camloc® and Dzus®) to secure one component to another.
At this time, the airworthiness concern is not considered an unsafe
condition that would warrant airworthiness directive action under Title
14 of the Code of Federal Regulations (14 CFR) part 39.
Background
Several incidents of engine cowl damage and resulting separations have
occurred across the Textron turbofan-powered airplane product line. The
separation incidents resulted in damage to the airplanes, and some
incidents have marginally affected airplane handling capabilities. The
FAA has not yet determined the root cause of these events but considers
maintenance error to be the primary contributing factor.
The Textron turbofan-powered fleet uses quarter-turn fasteners to
assemble the engine cowl system. The extent of the use of these
fasteners varies depending on the airplane model. Failure to verify
engagement of all quarter-turn fasteners can lead to cowl door damage
and/or separation due to the aerodynamic loads. Cowl doors that
separate from the airplane may strike empennage components, causing
structural damage and potential loss of airplane control.
This SAIB is intended to advise of the safety hazards and potential
dangers of inadequate and infrequent pre-flight inspections of the
quarter-turn fasteners used to attach engine cowling system components,
and of the need for routine preventive maintenance.
All inspections, checks, and processes should be accomplished in accordance with the manufacturer’s recommendations.
The FAA recommends thorough pre-flight by all pilots, and repetitive
inspections of the quarter-turn fasteners on engine cowl components.
All airplane owners and operators should acquaint themselves with the
configuration of the airplane, including the components that use
quarter-turn fasteners. Knowledge of the location and correct
installation configuration of quarter-turn fasteners will assist in any
pre-flight or repetitive inspection to identify fasteners that are not
normal or that may have changed since the last inspection.
In addition, engine maintenance activities require frequent cowl
removals. Our investigation indicates that a single inspection may not
always reveal an incorrect cowl re-installation. The FAA recommends a
second visual inspection of the complete engine cowl installation
immediately after a cowl has been removed and prior to returning the
airplane to service to ensure that all quarter turn fasteners have been
secured properly. Simple tools such as a ladder, flashlight, or mirror
may assist in the inspection process. A complete inspection should
consist of checking that all quarter-turn fasteners are correctly
seated and latched.
Typical areas to check and potential problems are:
- Improperly seated or improperly latched quarter-turn fasteners (most
installations have some quarter-turn fasteners in which the
installation cannot be viewed directly).
- Cowl doors with excessive forward edge gaps (distance to underlying
surfaces that exceed aero-smoothness requirements. Excessive mismatch
may result from quarter-turn fasteners with over- or undersized stud
lengths or cowl door repairs that increase the door thickness).
- Cowl door cracks that weaken the area around quarter-turn fasteners.
- Cowl door contour anomalies.
Repairs and Overhaul
Textron recommends replacing any
cowling system component that fails maintenance manual inspection
procedures or that is found defective (Ref. 14 CFR part 43 Appendix D,
(d) (11)). The FAA recommends verifying that each quarter-turn fastener
has been correctly repaired and replacing any fastener that has not
been correctly repaired. Additional information can be obtained from
Textron.
Each Textron airplane has aero-smoothness requirements that the cowl
door quarter-turn fasteners maintain. Improper quarter-turn fastener
installation, part replacements, etc., result in opportunities for the
cowl door aerodynamic load to lead to fastener failures and door
separation events.
Investigation by the National Transportation Safety Board, Textron, and
the FAA determined that these quarter-turn fasteners are frequently
repaired or replaced during the service life of the airplane. The
investigation also found that replacement quarter-turn fasteners often
do not conform to type design or an approved repair. These
nonconformities commonly include substitution of alternate parts or
combinations of different manufacture types, installation of
quarter-turn studs of inappropriate grip-length, and stud replacement
without commensurate receptacle replacement. It is also common for cowl
doors to have cracks that extend to or from a quarter-turn fastener
location.
The FAA strongly encourages consulting with a part 145 repair station
that has experience and expertise in cowl door inspection and repair,
prior to attempting the repair of any nacelle or cowl system component.
For Further Information Contact
Jeff Janusz, Supv Aviation Safety Specialist, 1801 Airport Road,
Room 100, Wichita, KS 67209; phone: (316) 946-4148; e-mail:
jeff.janusz@faa.gov.
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