Originally published by Paul Seidenman and David J. Spanovich for Aviation Week on August 11th 2016

Southwest Airlines is retrofitting all 583 of its Boeing 737NGs with special sensors supplied by Honeywell to gain additional data points to supplement Boeing’s Airplane Health Monitoring (AHM), which it installed on that fleet two years ago.

According to Ross MacArthur, fleet chief in the Dallas-based carrier’s Technical Operations Organization, Southwest noticed via AHM “that poor performance of the bleed air system was causing higher than acceptable service interruptions,” but there were a few key pieces of data missing.

“The vast majority—maybe 95%—of the data that will be needed for the engine bleed air monitoring will be available from the AHM,” he says. “However, we determined that we could justify the time and expense of the service bulletin work to install the sensors because of the additional data they would provide, which could prove to be of high value with monitoring of the bleed air system.”

Southwest Airlines plans to install engine bleed air temperature-monitoring sensors and supporting wiring on its entire Boeing 737NG fleet by 2017. Credit: Southwest Airlines

Southwest Airlines plans to install engine bleed air temperature-monitoring sensors and supporting wiring on its entire Boeing 737NG fleet by 2017. Credit: Southwest Airlines

For each engine, the sensors monitor the bleed air temperature as it comes from the engine. “What we are getting is a total of four (two per engine) data points—the bleed air temperature data, from the sensor installation, along with the bleed air pressure data, which we have had the ability to monitor with the existing software,” he explains. “Those four data points are now giving us insight into the health of the full bleed air system.”

The sensor upgrade project, which is slated for completion by 2017, requires the installation of supporting wiring and is being carried out during major checks, under a Boeing service bulletin. But MacArthur indicates that the airline might expand sensors to the 737NG cabin environment, and Southwest is working with Boeing on a cabin temperature monitoring solution now under development.

“This will again involve hardware and wiring modifications under an OEM service bulletin,” he says. “If we go ahead with the project, it will be as a result of what we have learned from the bleed air temperature sensors. And it’s possible that we could be the first 737NG operator to do this.”

Even for a modern commercial jet, MacArthur says, at some point the existing data provided by the AHM may not be enough to give a complete picture of aircraft system health. “That’s when an in-depth study must be carried out to determine the value of adding sensors,” he says.


Embraer says the cost of sensors depends on the technology. The lamb waves sensor costs less than $100 per data unit.  The comparative vacuum-monitoring sensor costs a few hundred U.S. dollars per monitored area.

Commercial engines, such as the CFM56, will have sensors for oil pressure, oil temperature, vibration and inlet temperatures as part of the engine’s type certificate. Replacement costs typically are in the $5,000-10,000-range per sensor, according to StandardAero’s Winnipeg-based engineering staff.

A standard BeanAir accelerometer costs €400-489 ($440-538), and a gateway €450-495. BeanAir also offers a starter package consisting of one device/sensor, one gateway and monitoring software, at a cost of €737-837, depending on options.  These products are available off the shelf, with multiple MRO applications, including ground vibration tests; landing gear, winglets and cabin vibration monitoring; and cabin comfort measurement, including temperature, humidity and tilt vibration.