Aircraft
Certification Service Washington, DC U.S. Department of Transportation Federal Aviation Administration
CE-10-10
November 30, 2009
This is information only. Recommendations
aren’t mandatory.
Introduction
This Special Airworthiness Information Bulletin is issued to inform you
of an airworthiness concern on Hawker Beechcraft Model 60 (Duke) Series
twin-engine powered airplanes.
At this time, this airworthiness concern is not an unsafe condition
that would warrant Airworthiness Directive (AD) action under Title 14
of the Code of Federal Regulations (14 CFR) part 39.
Background
After attempting to takeoff, a Hawker Beechcraft Model 60 (Duke)
airplane impacted terrain that resulted in the airplane being
destroyed. The flap actuators recovered at the crash site indicated
that the left flap was fully retracted and the right flap was fully
extended, which may have contributed to the accident. Further
examination of the flap actuators revealed evidence of
torsional-induced overload on the output shaft and corrosion on the
output drive shaft subassembly, key location, and roller bearings.
The roller bearings showed evidence of binding. Proper rigging is
essential to assure the correct operation of the flap system. If the
flap bottoms out in the flap track before the flap limit switch
deactivates the motor, it will stress the actuator, the 90-degree
output shaft, and key. Repeated cycles with this condition may result
in fractures in the key and output shaft.
The internal parts of both actuators were covered with a blend of oil
and bearing grease. While it is normal to have grease and oil present
in the actuator, the mixture of grease and oil on the actuator screw
may be an indication that grease had been used to lubricate the
actuator screw rather than oil. The Beechcraft Duke Model 60 Series
Maintenance Manual (P/N 60-590001-25) requires the actuator be
lubricated with MIL-L-6086 Grade M oil (gear oil) every 1,000 hours. In
addition, it requires that the actuator be replaced or overhauled every
2,000 hours. The Hawker Beechcraft Duke Model 60 Component Maintenance
Manual (P/N 60-590001-27) requires the bearings to be packed with
MIL-G-23827 grease before the actuator is reassembled.
Recommendations
The FAA recommends that owners, operators, and maintenance personnel
thoroughly review, understand, and adhere to the information published
in the documentation identified above to maintain the flap system in an
airworthy condition. Special emphasis should be placed on the correct
flap system rigging, actuator overhaul and inspection criteria, and the
use of the proper lubricants. Failure to do so can have serious
consequences.