Hundreds of Boeing 737 and 777 aircraft worldwide may be flying with unsafe systems five years after a US airline regulators warned that they could pose a crash threat. The problem affects 737s built before the Max range that are currently grounded following two fatal crashes. They include the popular Boeing 737-800 range as well as the 600, 700 and 900 aircraft.
US government officials in 2014 revealed that passenger mobile phones and other types of radio signals could pose a crash threat to some models of Boeing 737 and 777 aircraft.
Interference
More than 1,300 jets registered in the US were equipped with cockpit screens vulnerable to interference from wifi, mobile phones and even outside frequencies such as weather radar, according to the Federal Aviation Administration (FAA).
The regulator gave airlines until November of this year to replace the units made by Honeywell International.
That means that potentially hundreds of aircraft worldwide are still flying with the unsafe systems cited in the FAA report.
Ryanair has more than 400 next-generation 737s in its fleet.
Ryanair told the FAA in 2014 that its aircraft had 707 of the affected Honeywell units but it argued at the time that changing out all of them “is imposing a high, and unnecessary, financial burden on operators”.
A Ryanair spokesman said the airline had inspected all of its display units and “any affected DUs have been replaced”.
The FAA warned that flight-critical data including airspeed, altitude and navigation could disappear and “result in loss of airplane control at an altitude insufficient for recovery”, the FAA said in the safety bulletin, known as an airworthiness directive.
Honeywell hasn't heard of any blanking display screens caused by mobile phones or other radio frequencies while an aircraft was in flight, spokeswoman Nina Krauss said.
When airlines and Honeywell argued that radio signals were unlikely to cause safety problems during flight, however, the FAA countered that it had run tests on in-service aircraft – and the jets flunked.
Issues
Boeing first found the interference in a laboratory test in 2012. A company spokesman said it hadn’t seen similar issues on other aircraft.
Honeywell is aware of only one case where all six display units in a 737 cockpit went blank, Ms Krauss said. The cause was a software problem that had been fixed and was currently being flight-tested, she said.
The affected 737s are the so-called Next Generation model, a predecessor of the Boeing Max, which was involved in two crashes in less than five months. Cockpit displays on the Max were made by Rockwell Collins, now a unit of United Technologies, not Honeywell. Boeing's 777s also were covered by the FAA order.
The FAA order didn’t quantify the amount of radio signals needed to cause interference problems.
An agency spokesman said this week that the regulator based the compliance time for its airworthiness directives on the risk that a condition posed. “A 60-month compliance time frame means the risk is low, and does not need to be addressed right away,” he said. Still, the radio-signal threat extends beyond that specific display system and FAA warning.
Honeywell initially told the FAA that 10,100 display units – or the equivalent of almost 1,700 aircraft – were affected worldwide. When asked this week about the progress of the fixes, Honeywell’s Ms Krauss said that 8,000 components had been replaced and fewer than 400 needed upgrading.
The lower number reflects the fact that some airlines might have had the work performed at non-Honeywell facilities, and regulators in other regions of the world might not have ordered the units replaced. In addition, some aircraft might have been taken out of service due to age.
Depending on how many aircraft are still in service, the global number flying with display units that could cause critical data to disappear could be in the hundreds. But Ms Krauss said that “even if a blanking incident were to occur,” the units were backed up by multiple redundancies.
Both Delta Air Lines and Southwest Airlines have completed their overhauls, according to the companies. American Airlines has 14 more jets that need refurbished units, and United Airlines still needs to replace components across 17 aircraft, representatives from those companies said.
‘Disastrous’
In just the past three years, mystified pilots flying Boeing NG or 777 jets – the same models cited in the FAA warning on mobile phones – have reported more than a dozen instances of important flight information disappearing. Calling the situations "critical", the pilots filed their concerns with the Aviation Safety Reporting System, or ASRS, which is administered by Nasa.
Last September, pilots of a 737-700 noticed that various flight information was flashing on and off, and showing different air speeds and altitudes. Then a primary display unit went blank. “At that time,” the pilots wrote, “we decided it was best to get the aircraft on the ground.”
In January 2017, pilots of a 737 flying out of Costa Rica lost all of their map displays and the flight-management computers on both sides of the aircraft “during a critical phase of flight in mountainous terrain”, according to the crew’s ASRS report.
If the flight information had disappeared in bad weather or at night, “it could have been a potentially disastrous outcome”, the pilot wrote.
Later that year, the captain of a 737-800 reported that key flight data intermittently disappeared as the jet was climbing through turbulence and the screens blanked even more during the descent. After the aircraft landed, maintenance crews couldn’t find any reason for the blanking display units.
“Due to no known cause for a known recurring problem,” the pilot reported to ASRS, “I refused the aircraft for the next leg.”
The Nasa-administered database scrubs the reports of identifying details, including names of airlines, pilots and usually the locations. Aviation experts caution that the ASRS filings are based on crew reports and don’t provide official findings.
And blanking display screens haven’t been cited in crashes, only in scary incidents.
Two years ago, the pilot of a 737-800 reported multiple episodes of important flight information “blanking or simply not functioning,” including an incident where the aircraft flew into a wind shear due to lack of data. “The so-called momentary blanking”, the pilot wrote, “is a puzzle”. – Bloomberg
