US operators of Boeing 747-400 Freighters have stepped up aileron inspections to address a recurring problem involving wear and other damage to aileron attachments.
That is according to the US National Transportation Safety Board (NTSB), which says in a newly released report that fractured aileron attachments caused an inflight issue involving a Kalitta Air 747-400F in 2024.
That event prompted the NTSB to ask other carriers if they had experienced similar issues; two operators said they had, according to the report, which does not specify those airlines’ names.
The incident involved a Kalitta 747-400F (registration N782CK) operating a flight from Spangdahlem air base in Germany in Hong Kong on 17 August 2024.
After taking off and ascending through 25,000ft, while flying at about 334kt (619km/h), the 747’s pilots noticed an unusual vibration that prompted them to level off and reduce speed, after which the vibration stopped, says the NTSB’s final accident report.
The vibration returned after the aircraft started ascending again. The pilots also noticed that the jet’s engine-indicating and crew-alerting system showed that the right outer aileron was defected downward 2° more than the left. The ailerons should have been locked at neutral, the NTSB says.
Others pilots onboard but not flying the 747 looked at the window and reported “the right-hand outboard aileron vibrating”, Kalitta said in a September 2024 letter to the NTSB.
The pilots diverted to Istanbul and landed without incident.
Right outboard ailerons on 747-400s connect to the wing at six attachment points; five of those attachments are composed of a “hinge-rib installation” connecting to the wing and a “fitting and retainer assembly” connecting to the aileron’s leading edge.
An inspection following the flight revealed that three of the five hinge ribs had “fractured”, a condition that “would adversely affect the structural strength of the aileron”, the NTSB says. The fractures were due to fatigue.
Inspections also revealed that improper cable tension caused the right outer aileron’s deflection.
The incident prompted Kalitta to inspect its other 747-400Fs. The airline has 23 of the jets, according to fleet data provider Cirium.
“These inspections revealed that numerous airplanes exhibited low cable tensions in the aileron control system, and nearly all airplanes displayed hinge wear on both the wing and aileron sides that exceeded component maintenance manual limits,” says the NSTB.
It adds that two other US 747-400F operators subsequently reported ”instances of wear and damage to aileron hinge fittings and related components”.
One of those, after reviewing 10 years of fleet data, reported “multiple flight control cable-related issues, including significant out-of-limit cable tensions, prompting the implementation of routine tension checks across their fleet”, the NTSB says.
The other airline reported “several hinge assembly replacement since 2008”.
Besides Kalitta, US operators of 747-400Fs include Atlas Air, National Airlines and UPS, Cirium shows.
