Honeywell Works to Improve Air Turbine Starter Reliability

You never give the starter on your car a second thought until it fails. The same is true with the air turbine start system (ATSS), the reliable system used to start the turbine engines that power all kinds of aircraft. Honeywell’s ATSS already sets a high bar when it comes to system reliability. In fact, the mean time between unscheduled removal (MTBUR) rate for our ATSS is around 60,000 operating hours. In spite of that impressive number, Honeywell engineers are constantly looking for ways to take ATSS reliability to the next level.

In the rare event the ATSS or one of its components fails to start, it causes frustrations for operators, pilots, maintenance teams, and passengers. One such starter component that can fail on occasion is the clutch.  Honeywell has developed a decoupling output shaft to prevent secondary damage from occurring after a clutch failure. In the event of clutch failure, the decoupling output shaft “decouples,” separating the starter from the engine backdriving force, thus eliminating the additional damage that occurs from a backdrive event.

If the ATS clutch fails, the engine and starter will not disengage after the engine has started, causing the engine to back drive the starter. This is known as “backdrive” failure.  Backdrive events generate significant heat and damage to the starter, typically breaching the housing, leading to the oil loss, including engine oil loss if it is a shared lube system, and in worst case, engine fire.

Over the years, Honeywell has perfected the output shaft design to eliminate risk of inadvertent decoupling events.  Inadvertent decoupling event occurs when an output shaft decouples even though a clutch failure has not yet occurred.

For example, we recently improved the B737NG/CFM56-7 decoupling output shaft.  11,500 starters have been upgraded to the latest design – equivalent of 82% of fleet. No inadvertent decoupling event has been reported for starters with latest output shaft design. Other improvements are in the works as Honeywell looks to create a new generation of ATS systems that will be even smaller, lighter, smarter, more reliable and more connected.