The Bombardier Learjet 40 and 60 have been attracting attention after one Learjet 60 operator recently raised word of a potential fire hazard that exists whenever power is applied to the aircraft battery charging bus.
“It is possible for power to be applied to the horizontal stabilizer anti-ice boot parting elements with the aircraft on the ground and the stab/wing heat switch in the ‘off’ position if there is power on the aircraft battery charging bus (battery switches on/APU on),” he wrote. “Furthermore, the only indication in the cockpit may be a higher than normal current draw on the APU amp meter.”
AIN has found several operators who have experienced the same problem. Apparently the failure point is a remote control circuit breaker (RCCB) that is normally open but fails in the closed position, allowing 28 volts from the aircraft battery charging bus through the 50-amp current limiter directly to the parting element.
The aircraft uses three RCCBs; two of them control the flow of power to the left and right parting elements, and the third controls power through a solid-state timer. It is possible for a fire to occur with no indication in the cockpit to alert the crew. One of the operators reported that such a fire resulted in damage to the leading edge of the right horizontal stabilizer, requiring it to be replaced.
In an unrelated mechanical misfortune, another operator complained of three starter-generator bearing failures in 2,240 hours of operation in his Learjet 45. All three resulted in in-flight engine shutdowns. “The last two that failed had roughly 900 hours on one and 1,000 hours on the other.”
Kevin Polian, v-p of customer support and warranty for Bombardier Learjet, told AIN, “Recent comments made on the NBAA Web site regarding a problem with the Bombardier Learjet 60 horizontal stabilizer anti-ice heating elements and with the Learjet 45 starter generator prompted lively debate on the Web site and resulted in some speculative comments regarding Bombardier’s ability to respond to issues with their Learjets.
“Bombardier has been working with its suppliers for the past six months or longer to fix both issues,” he added.
“We anticipate that both of these issues will be fully resolved this year,” Polian said. He added that for the Learjet 60, “We are actively pursuing a solid-state circuit breaker to replace the existing one as well as an indication in the cockpit if the system self-activates for whatever reason.”
Polian said Bombardier is also addressing the Learjet 45 starter-generator issue, and a change in the bearing replacement interval is imminent. “This component had a 1,200-hour overhaul cycle and some operators were seeing bearing failure at 600 hours or less,” he said.
“Recent data indicated that the 600-hour bearing replacement was more prudent from an overall reliability standpoint.”
Finally, Polian conceded that Bombardier needs to work on its customer-interaction system. He said, “Moving forward, to avoid misconceptions such as these and to re-establish communication clarity with our aircraft operators, we will improve our advisory wires, report progress on our NBAA top 10 Learjet issues in our Customer Forum Newsletter; and overall, ensure our operators are advised on all issues on a regular basis.”