The head of an airline advocacy group warned officials at Heathrow Airport of the threat posed by potential substation failures days before a fire forced the shutdown of the airport last month, he told British lawmakers on Wednesday.

“I’d actually warned Heathrow of concerns that we had with regard to the substations,” Nigel Wicking, the chief executive of the Heathrow Airline Operators’ Committee, the advocacy group, told the parliamentary transport committee. “My concern was resilience.”

A fire at one of the three electrical substations that serves Heathrow, Europe’s busiest airport, led to a power outage there on March 21.

The shutdown dashed holiday plans and scrambled flights across the world, and Mr. Wicking said that he thought that some flights could have resumed by “late morning” if the airport had made better use of one of its five terminals.

“Flights could have been brought in,” he said, speaking of flights that were stuck in Europe and elsewhere, adding that the airlines had been pushing to bring planes to London much quicker.

The fire at the substation raised questions about the vulnerability of Britain’s infrastructure, and experts have said it could cost up to $100 million to create backup systems that could have kept the airport running during such a catastrophic power failure. Such a project could also likely take years to put in place.

But some of the issues surrounding the concerns about the substation were more mundane: For instance, Mr. Wicking said, there had been incidents of theft around the power supply at the substation.

On one occasion, he said, it “took out the lights on the runway for a period of time.”

“That obviously made me concerned,” he added, noting how important Heathrow is to air trave not just in Britain and the broader European region but around the world.

“We need to make sure it is resilient,” he said.

This is a developing story. Check back for updates.