Some Learjet 40* and Learjet 45* aircraft operators have been experiencing various ongoing intermittent bleed air issues. While some are false indications, many are actual leaks.
These indications are more noticeable with, but not limited to, Learjet 45 aircraft equipped with APUs during hot weather operations.
Bombardier has issued several Service Bulletins (SBs) to resolve these issues.
The following SBs address the bleed air indication issues.
Inspection/ Modification of the APU Bleed Air (E25) and Anti-Ice (E27) Detection Elements
This SB inspects the E25 & E27 bleed leak elements for proper routing and corrects as necessary.
Bleed Air and Anti-Ice Leak Detect Element Spacing and Standoffs
This SB installs additional clamping and insulators along bleed leak detect elements along with a support bracket.
Inspection/ Replacement of Bleed Leak Detect Units.
This SB inspects/replaces some units that may have faulty PC Boards that can cause false indications (CAS Messages) with a more reliable unit.
Replacement of the Pylon High Pressure Bleed Air Manifold Switch
This SB lowers the trip point of the HP Switches from 130 (+/- 5) psi to 105 (+/- 5) psi, which lowers the switching of the LP air to HP air at a lower thrust.
Installation of APU Tailcone Ventilation Fan Thermostats.
This SB adds thermostats closer to the APU to activate the existing factory ventilation fans on hot days.
Tailcone Overheat Protection System (TOPS)
This has been proven by a large part 135 fleet operator to greatly reduce APU shut downs in hot climates when the aircraft is sitting on the ramp with the APU running.
The following SBs address Pylon Overheat CAS Messages
Replacement of the Pylon Heat Blankets
This SB reduces pylon overheat CAS messages associated with heat radiated from the bleed air ducts.
Removal of the Nacelle Anti-Ice Valve Heat Blankets
This SB removes the heat blanket previously installed by SB 45-36-08/ SB 40-36-04, Revision 3 or earlier. When the heat blankets were installed on the anti-ice valves, they may have inadvertently reduced the life of the valves.
All of the above Service Bulletins are about indication issues only. They do not address leaks. That is for next month with Part II-Leaks and another list of SBs.
*Trademarks of Bombardier Inc. or its subsidiaries
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