The US Federal Aviation Administration is requiring airlines take steps to a prevent a potentially dangerous slat issue that could affect Boeing 787s operating in winter weather.
An airworthiness directive (AD) made public on 11 October requires airlines to instruct pilots not to retract 787 flaps after landing in conditions involving snow, ice or slush.
The order also instructs airlines to inspect outboard slats and flaps after 787s land in such conditions.
"Boeing discovered that 787 slat operation could potentially be affected by ice during winter operation," Boeing says in a statement. "The issue is a hypothetical event that has never occurred in service. The probability of this issue occurring is very remote."
Boeing addressed the issue in a July service bulletin and is now "developing an actuator and/or sensor change for operators to identify and fix the issue", it says.
"Additionally, Boeing is providing direction for annual inspection of slat system health, re-emphasising existing procedures associated with winter operations, and [providing] additional maintenance procedures for a slat operational check," it adds.
The FAA's AD takes effect immediately, though it is accepting comments until 25 November. The AD applies to 787-8s, 787-9s and 787-10s.
The agency issued the order in response to reports that five 787 slat actuators failed when aircraft were taxiing, causing the slats to be in a position different from that commanded by the pilots.
"This condition, if not addressed, could result in insufficient lift, resulting in inability to maintain continued safe flight and landing," the FAA's AD says.
After landing in snow or ice, an airline's ground technicians should retract the flaps only after inspecting the slats and flaps to ensure they are not obstructed by ice, snow or slush, the AD says.
Two technicians should then test the slats – one moving the flap control lever and the other confirming the slat position.