The US Federal Aviation Administration (FAA) has proposed some changes on the overhead panel and wiring for Next Generation Boeing 737 aircraft.
This follows reports that three pilots failed to manually activate air data sensor heating systems on the aircraft as part of a pre-takeoff checklist procedure. Air data sensor heating systems include pitot tubes that may provide incorrect airspeed information to the flight deck if they are blocked by ice.
"The affected airplanes do not have an automatic activation of the air data sensor heating system," said the FAA. "Pilots activate the system manually as a pre-takeoff checklist item. Failure to activate the air data sensor hearing system could result in ice formation on air data system sensors, which could lead to misleading airspeed data or loss of all airspeed indicating systems, and loss of control of the airplane."
The proposed airworthiness directive (AD) will necessitate operators to make overhead panel and wiring changes that will ensure continuous power supply to pitot tubes, angle-of-attack sensors and total air temperature probes throughout the flight.
After these changes, the "on" and "off" probe heat toggle switch positions on the overhead panel will be replaced by "on" and "auto" positions. When the switch is set to "auto", electrical heat will be provided to the sensors at all times.
According to FAA estimates, these changes would take 80 hours per aircraft to implement, and will cost about $15 million for the 1,025 Boeing 737-600/700/700C/800/900/900ER aircraft in the US-registered fleet. These changes would need to be implemented within two years.