Aircraft
Certification Service Washington, DC U.S. Department of Transportation Federal Aviation Administration
CE-10-44
August 9, 2010
This is information only. Recommendations
aren’t mandatory.
Introduction
This Special Airworthiness Information Bulletin alerts owners and
operators of Cessna Model 402C airplanes of an airworthiness concern,
specifically a reminder of the meaning of the “HYD PRESS” indication,
and what may happen if this indication is not addressed.
At this time, the 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
Six minutes after takeoff from a busy airport, a pilot reported
smoke in the cockpit and declared an emergency. The aircraft landed
without incident and all passengers and crew deplaned successfully.
Maintenance determined that the hydraulic pressure did not relieve due
to the nose gear not fully retracting. The nose strut did not extend
completely, which prevented the nose gear from going in the up and
locked position. This caused the hydraulic system to remain
pressurized, which caused the fluid to heat up enough to melt the
hydraulic reservoir sight tube. The hot hydraulic fluid then spilled
out into the nose baggage compartment, releasing fumes into the cockpit
and causing the perceived smoke.
The Model 402C uses a hydraulically actuated landing gear system. When
the landing gear is locked Up or Down, the hydraulic fluid is
continually circulated through the system by the engine driven
hydraulic pumps at a nominal pressure up to 50 psi. When the gear is
selected from one position to another, the pressure varies but can
reach as high as 1750 psi. When the system is pressurized above 150-175
psi, a pressure switch in the system activates an annunciator light
(“HYD PRESS”). This light indicates that hydraulic pressure is flowing
to the landing gear system. Any time the landing gear is in transit,
the HYD PRESS annunciator should be illuminated.
Although we were unable to verify this, the HYD PRESS light in the
above incident should have been illuminated starting at the time when
the pilot selected gear Up, and should have remained illuminated for an
extended time because the nose gear did not fully retract.
Cessna has since released temporary revisions (TRs) to the pilots
operating handbook (POH) for this aircraft with the following
information:
To make it easier for pilots
to find the correct procedures, the procedures for “Hyd Pressure Light
Illuminated After Gear Cycle” were moved from Landing Gear Emergency
Procedures to Hydraulic System Emergency Procedures (this new section
was created by the TR).
A Caution statement was
added to the Amplified Procedures to emphasize that if the hydraulic
system remains pressurized for an extended period of time, the sight
tube could rupture. (Previously, the POH stated without a Caution
statement that damage to the system was possible).
The Emergency Procedures,
both the Abbreviated and the Amplified procedures, for “Hyd Pressure
Light Illuminated After Gear Cycle” were enclosed in a box, making them
immediate action items that are to be committed to the pilot’s memory.
This point is especially important because this issue is most likely to
occur shortly after takeoff, when the pilot is busy. If this were to
occur, the pilot should not have to look through the POH in an attempt
to find the correct procedure to address the indication; the pilot
should already understand the issue and know how to resolve it.
Recommendations
We recommend that pilots do the following:
Incorporate the TRs above into your POH; and
When the HYD PRESS light
remains illuminated for an extended time (longer than the normal
landing gear cycle time), complete the procedures for “Hyd Pressure
Light Illuminated After Gear Cycle” that they previously committed to
memory. Please see the TRs to the POH for these procedures. Delaying
completion of the procedures could result in damage to the hydraulic
system and smoke/vapors in the cockpit.