Parking planes during the pandemic doesn't mean technicians ignore them until airlines are ready to fly again. A great deal of mechanical support work, including electrical checks and engine starts, takes place to keep aircraft serviceable.
Even when approved maintenance schedules are followed, there are threats to the safe return of aircraft from extended downtime.
The U.K. Civil Aviation Authority (CAA) recently issued a safety notice addressing the potential hazards of bringing aircraft out of storage as airlines resume more flights.
The agency said it found examples of incomplete maintenance and other faults associated with lengthy storage of aircraft, including two cases involving loose engine ports and a missing access panel to a wing flap.
In another recent case, mechanics found insect larvae in instruments that help determine an aircraft's airspeed even though the probe's covers had been used and the system flushed according to the manufacturer's guidance.
The CAA also alerted operators that inappropriate dosage of the fuel biocide Kathon could lead to engines idling too slowly and to be on the lookout for unexpected corrosion of certain safety systems, such as the engine bleed air valve on the Boeing Co. (NYSE:BA) 737 Next Generation.
Other unforeseen technical snags airlines and repair organizations have identified include water ingress with Airbus A350 pressure release shut-off valves, emergency battery failures across various types of aircraft and problems with air conditioning packs, said Andrew Doyle, director of market development at data analytics and air travel research firm Cirium, on a recent webinar he hosted.
To avoid those types of problems, Cathay Pacific recently announced it will be transferring about a third of its fleet from hot and humid Hong Kong to a dry, desert field in Australia to help preserve them and keep moisture from forming in the fuel tank.
Airlines placed most of their fleets in a state of hibernation when COVID-19 spread worldwide in March and travel demand evaporated. Precautions include sealing up the engines and sensors to keep out dirt, birds and insects. Engineers frequently check wings and landing gear areas for wildlife. Rodents can damage wires and hydraulic lines.
The top three storage locations are in the U.S.: Roswell International Air Center in Nevada; Pinal County Airpark in Arizona; and Victorville Southern California Logistics Airport, with about 900 planes combined, according to Cirium.
The percentage of passenger jets in storage continues to fall, but a third of the global fleet remains grounded. As of Aug. 10, Cirium classified a total of 8,750 widebody, narrowbody and regional jets in storage status, while nearly 17,500 were in service. During the spring, more than two-thirds of the global feet was in storage.
Recent outbreaks and the end of summer vacations are dampening bookings and forcing airlines to slow their restart campaigns.
Airlines are bringing back their newest aircraft first because of better operating efficiencies. Cirium said that fewer than half of passenger jets built prior to 2013 were used for commercial flights two weeks ago. The most active aircraft were built in 2017. The grounding of the Boeing 737 MAX fleet left fewer 2018 aircraft available for service, it noted.
Airlines are also prioritizing narrowbody aircraft because most of the uptick in travel demand is on shorter domestic and regional routes. Only 29% of the global fleet remains inactive, while 37% of regional jets and 43% of wideobodies have yet to return to duty, Cirium said.
The maintenance status of an aircraft dictates which aircraft airlines fly, said Rob Morris, global head of consultancy at Cirium. "Aircraft that are close to a major check or an engine shop visit are clearly going to be less attractive to bring out of store because the cost of returning them to service will be significant."
The longer aircraft are in storage, the more likely they are to require heavier maintenance work before they can return to service, ranging from software and technical updates to following airworthiness directives and service bulletins, said Johan Bank, senior consultant at VZM Management Services.
Chris Markou, head of operational cost management at the International Air Transport Association, noted that "there are licenses expiring and certifications that are going to be outdated. Inspectors and mechanics cannot access aircraft due to quarantine measures, travel bans and other restrictions."