Honeywell cockpit display units that experienced interference from wi-fi signals on certain Boeing aircraft flickered and went blank for as long as six minutes, a proposed rule from the Federal Aviation Administration (FAA) states.
The issue of the blanking Honeywell phase 3 display units--which provide critical flight information to pilots such as airspeed, altitude, heading and navigation--was first revealed in 2011 after the interference was discovered during tests on the ground. The screens blanking could cause pilots to lose this information during critical phases of flight and lead to loss of control of the aircraft, the proposed directive says.
The FAA’s proposed rule, which is open for industry comment until 8 November, applies to about 157 aircraft registered in the USA with the phase 3 generation displays. This includes Boeing 737-600s, -700s, -700C, -800, -900, -900ER and 777 aircraft. The proposed rule is open for comments until 8 November.
The displays showed susceptibility to the emissions of the wi-fi frequencies at “radiated power levels below those that the displays are required to tolerate for certification of a wi-fi installation,” the AD states.
The issue of screens blanking out has not been known to occur on any flights, says Honeywell.
“No display units have ever blanked in flight due to wi-fi interference,” says the supplier. “The only know occurrence was during a developmental test conducted on the ground. We worked with Boeing and addressed any concerns in 2012 with new display hardware. “
The extent to which the electro magnetic interference affected the Honeywell display units is atypical, says a company that has performed tests of the units.
“We have witnessed other interferences, but none that have come anywhere remotely close to approaching the critically of the Honeywell Phase 3 display unit,” the firm tells Flightglobal on the condition of anonymity.
To comply with the airworthiness directive, airlines would have to install new software and replace the phase 3 common display systems on the 737s and 777s with new versions known as the 3A model.
Boeing says it began installing updated versions of the displays in September 2012 on production aircraft and released service bulletins with instructions for retrofitting the displays on the older aircraft in November of that year.
After the problem was discovered, placards were placed in the flightdeck of affected aircraft that instructed pilots not to use wi-fi in the cockpit until the new 3A displays and accompanying software were upgraded, says Boeing.
Once operators complete the upgrades to the 3A displays on those aircraft, pilots can resume using the wi-fi in the cockpit for flight-related functions like electronic flight bag (EFB) functionality.