A blaze at a substation near the airport caused the closure on March 21, raising questions about the resilience of national infrastructure.
The incident left about 300,000 people stranded and cost airlines millions of pounds.
Seeking to learn lessons, MPs on Wednesday quizzed the chief executive of Heathrow and senior representatives from National Grid, power provider SSE and an airline representative.
Nigel Wicking, boss of the Heathrow Airline Operators' Committee that represents 90 airlines using the hub, said he had voiced concern on March 15.
"I'd actually warned Heathrow of concerns that we had with regard to the substations, and my concern was resilience," Wicking said.
He raised further concerns two days before the fire after the lights of one of Heathrow's runways went out for a short period following theft of cable.
Safety was the main concern for Heathrow, Thomas Woldbye, the airport's CEO said.
The fire meant the airport had to power down systems, then rewire the airport to connect to another power supply, before powering back up, and that took hours.
Wicking said the airport could and should have started flights sooner.
"I'm not hearing that there was a lack of power to come into Heathrow," he said.
"I was hearing that it took time to move that power to where it needed to be within Heathrow. And 10 hours for me, were too long."
The airport's contracts with power suppliers had resilience built in, Woldbye said.
Building full resilience at the airport would come at a very high cost, he said, estimated at Stg1 billion ($A2 billion).
