Thu, Feb 09, 2012
Bulletin Follows Reports Of Pitch Trim Freezing
The FAA has issued a Special Airworthiness Information Bulletin
(SAIB) following reports of pitch trim freezing on four Citation
Mustang airplanes, and offers recommendations to prevent the issue
from occurring. At this time, the FAA says the airworthiness
concern is not an unsafe condition that would warrant the issuance
of an AD.
There have been at least four reports of pitch trim systems
(electric and manual) freezing in flight. In three of these events,
pitch trim was recovered in flight either by descending to a lower
altitude or forcing the pitch trim loose with the manual wheel. In
most cases, the airplane had been exposed to precipitation, and the
pilots had reported seeing a primary flight display annunciation
(indicating elevator mistrim or electric elevator trim
inoperative). In one case, a pilot reported large amounts of water
draining from the tailcone for at least 45 minutes after
landing.
Cessna has released two mandatory service documents to help
remedy this issue. In March 2010, Service Letter (SL) 510-53-03 was
released. This SL called for an inspection of the tailcone lower
skin assembly to verify the presence of a drain hole. If the drain
hole was missing, the SL specified it to be installed. In February
2011, SL 510-55-02 was released. This SL called for installation of
sealant along the fairing at the top of the vertical stabilizer,
around the ground recognition light, and optional high frequency
antenna.
In addition, Cessna had Garmin inspect a servo and servo mount
that had been involved in one of these events. In the servo mount,
Garmin found an oily substance on the slip clutch rings and
friction disks. This substance, which was found to be lubricant,
reduced the torque output capability substantially.
The FAA recommend that owners and operators of Cessna Model 510
(Citation Mustang) airplanes ensure that pilots review and follow
the appropriate Abnormal Procedures in the airplane flight manual
(AFM )(electric elevator trim inoperative, elevator mistrim, and/or
jammed elevator trim tab) if a loss of pitch trim occurs in flight.
Maintenance personnel should perform both SL 510-53-03 and SL
510-55-02 on all affected aircraft to ensure appropriate drainage
and sealing in the affected areas. The agency further recommends
that owners and operators should ensure that maintenance personnel
have performed and continue to perform maintenance manual Task
22-10-20-720 (Autopilot Servo Mount Functional Check) every 450
hours or 12 calendar months, whichever occurs first.
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