Crews that operate Boeing 777 and 787 aircraft have been notified about misleading pitch guidance during glideslope interference on instrument landing system (ILS) approaches. The Federal Aviation Administration (FAA) issued this warning of potential erroneous autopilot flight director system (AFDS) guidance in a special airworthiness bulletin on April 16th.
FlightGlobal initially reported the bulletin, stating that Boeing 747-400, 747-8, 757, and 767 operators have also been cautioned about the issue. The FAA’s investigation shows that misleading pitch guidance occurred at the same time as glideslope signal interference and, in the majority of cases, during glideslope capture. ILS signal interference can occur when vehicles and aircraft impact the localizer or glideslope signal.
According to the FAA, service history indicates flight crews may follow misleading AFDS guidance after disconnecting the autopilot. This situation could potentially result in dangerously steep approaches short of the runway. Additionally, there could be long approaches resulting in late touchdowns and possible runway excursions.
Despite the concerns, the FAA feels that the situation is safe enough, so there won’t be a warrant of an airworthiness directive (AD). The group states that Boeing has issued a manual that provides instructions to crew in the event of these issues. This guidance was released last fall.
“The Boeing Company issued Boeing Flight Crew Operations Manual Bulletin S489-50, dated October 18, 2019. This operations manual provides operating instructions for AFDS operation during periods of localizer or glideslope signal degradation or signal instability, and the possible flight deck effects during such an event,” the FAA said in its bulletin.
“The operating instructions reinforce existing procedures and training.”
Boeing is working with its supplier to develop operational program software to correct misleading flight director guidance. Furthermore, the FAA is thinking about issuing rulemaking to mandate the application of the software once it is ready.
Until then, the FAA recommends that all owners and operators of the aircraft mentioned in its bulletin respond to the suggestions outlined in Boeing’s operations manual as soon as possible.
Altogether, this news follows a tough year for Boeing following its well-publicized safety problems surrounding the 737 MAX. The issues highlighted this week are not thought to be as critical. However, the manufacturer will be looking to resolve the situation as soon as possible.
Simple Flying reached out to Boeing for comment on the warning issued by the FAA but did not hear back before publication. We will update the article with any further announcements.
What are your thoughts about the advice from the FAA? Are you concerned about these issues with the AFDS system? Let us know what you think in the comment section.