Boeing Changes 737 Wiring, Checklists After Airspeed Incidents

By John Croft
Source: AWIN First

The agency recommends that the FAA and Boeing review the design and operation of the pitot heat indicator system for the Boeing 737 with respect to latent failures, as well as make changes to the aircraft’s quick reference handbook (QRH) to consider other systems that might be affected by a pitot failure, including spurious stick shaker activations.

The AAIU says that Boeing, after being given a draft of the final report, said it had analyzed ways to improve the reliability of the indicating system for the probe heaters. “It found that by reversing the connection polarity of the probe heat wiring, a partially shorted probe continues to provide adequate heat until the short burns through the wire element thus causing an open circuit (and associated indication). This has been verified via analysis and testing of a shorted probe.”

Boeing says the wiring change is now included in new production aircraft, and that it plans to release a service bulletin in the first quarter of 2014 for making the changes on existing 737 next-generation models. Coming in June 2014 will be an amended checklist that will include “various symptoms of possible unreliable airspeed including the activation of stick shaker,” says the AAIU.

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