Several Australian registered Cessna 208 aircraft are operating
under Australian Civil Aviation Safety Authority Approved Single
Engine Turbine Powered Aeroplane (ASETPA) authorisation without an
aircraft manufacturer approved safety enhancement. The safety
enhancement requires the aircraft Emergency Power Lever (EPL) to
have copper witness wire installed to prevent inadvertent
activation during normal operations, and to indicate movement of
the lever during emergency use. Inadvertent activation of the EPL
during normal operations could cause engine surging, exceeding
inter-turbine temperatures, gas generator speeds and torque limits,
leading to engine damage.
The EPL, which is connected through linkages to the manual
override lever on the fuel control unit, governs the fuel supply to
the engine should a pneumatic malfunction occur in the unit. The
EPL permits the pilot to restore engine power by activating the
lever to manually introduce fuel to the engine.
The aircraft manufacturers Service Kit, SK208-142, provides for
the installation of mechanical devices allowing for the
installation of copper witness wire to the EPL. If the EPL has been
moved from the NORMAL position, the copper witness wire will
fracture and provide a physical indication that it has been
activated. The installation of Service Kit SK208-142 is not
mandatory for Australian registered aircraft.
Cessna Alert Bulletin, CAB01-15, includes a requirement to ensure
the fitment of the copper witness wire to the EPL of all aircraft
that have had Service Kit SK208-142 installed. Some Australian
operators have had Service Kit SK208-142 installed in their
aircraft, but are not complying with the Cessna Alert Bulletin
CABO1-15 as it is not mandatory for Australian registered aircraft.
Compliance with the requirements of the bulletin was also not
mandated by the US Federal Aviation Administration.
The aircraft maintenance manual states that if the EPL witness
wire was broken or missing then a determination was to be made, as
required by the engine maintenance manual, to ascertain if the
engine limitations had been exceeded.
The aircraft pilots operating handbook includes a caution that
'The emergency power lever and its associated manual override
system is considered to be an emergency system and should be used
only in the event of a fuel control unit malfunction. When
attempting a normal start the pilot must ensure that the emergency
power lever is in the NORMAL (full aft) position; otherwise, an
overtemperature condition may result.
'When using the fuel control manual override system, engine
response may be more rapid than when using the power lever.
Additional care is required during engine acceleration to avoid
exceeding the engine limitations.
'Inappropriate use of the emergency power lever may adversely
affect engine operation and durability. Use of the emergency power
lever during normal operation of the power lever may result in
engine surges, or exceeding the ITT, Ng, and torque limits.'
Inadvertent movement of the EPL during normal operations could
result in engine damage. Compliance with the requirements of
CABO1-15 would mitigate the risk of such an inadvertent movement
and would ensure that appropriate maintenance actions were taken as
required by the engine manufacturer.