Experts are warning airlines to take extra care when reactivating planes left in storage during the pandemic.
Pilot rustiness, maintenance errors and even insect nests could be potential dangers for aircraft re-entering service.
Travel restrictions have caused a huge decline in flying, with many planes put in extended storage.
As a result, there has been a spike in the number of reported problems as planes return to service.
“Every aircraft is going to have a specific set of instructions for maintenance, but it has never been done on this scale before,” said Greg Waldron, Asia managing editor of aviation magazine FlightGlobal.
Along with regulators, insurers have also expressed concern. “We’ve got people returning to work who are quite rusty, which is a big issue,” said Gary Moran, head of Asia aviation at insurance broker Aon.
Not 'like riding a bike'
One of the most worrying problems is an increase in the number of poorly-handled landing approaches.
The number of so-called "unstabilised approaches" has sharply increased this year, according to the International Air Transport Association (IATA).
They can result in hard landings, runway overshoots or even crashes.
In May, a Pakistan International Airlines jet crashed after an unstabilised approach, killing 97 people, while 18 died in an Air India Express crash on landing in August, also after an unstabilised approach.
Experts say that pilots might need to be more cautious than usual as they re-enter service.
“Flying an aircraft can be quite technical. If you haven’t been doing it for a while, it’s certainly not second nature like riding a bike,” Mr Waldron added.
However, he said airlines are aware of the issue and in many cases have booked extra time for their pilots in flight simulators.
Aircraft in storage typically undergo a routine maintenance schedule to ensure they're ready to return to service when business improves.
Asia Pacific Airline Storage, which has a facility at Alice Springs that stores planes for Cathay Pacific and Singapore airlines, employs more than 70 maintenance crew.
Manufacturers also give very detailed instructions about how to store their aircraft. But there have still been some reported problems.
For example, the European Union Aviation Safety Agency (EASA) said there has been a surge in the number of reports of unreliable airspeed and altitude readings during the first flight after a plane leaves storage.
In some cases, take-offs have had to be abandoned or the aircraft has had to return to base.
In many previous cases problems with airspeed readings have been due to insects or larvae in the aircraft's pitot tubes, which are key components used to measure air speed.
These issues are well known within the aviation industry, and Mr Waldron said he thinks airline travel will remain safe.
But he added that there will be some issues, because planes have been stored for longer than before, and in some cases the planes in storage are new models, which means the potential issues are not as well documented.