Shares in Boeing fell 4.7% as investors reacted to news of a fire on one of its 787 Dreamliner aircraft.
The stock tumbled as much as 7% immediately after news of the fire at Heathrow Airport, but eased back later.
Earlier this year, problems with batteries on Dreamliner aircraft led to the grounding of the fleet and forced Boeing into a costly re-design.
The company's shares had been trading at a 52-week high on Friday before news of the fire first broke.
Companies supplying parts of the Dreamliner, including Honeywell and Rockwell Collins, were also hit. The fall in Boeing's stock was its biggest one-day drop since August 2011.
"If we learn this is from the battery, it is a very big problem" for Boeing, Bloomberg Industries' senior aerospace analyst George Ferguson told the BBC.
Boeing has not yet disclosed the full cost of resolving the Dreamliner's battery problems and any compensation for customers.
The entire fleet of 50 787s in service was` grounded in January for problems involving the aircraft's lithium-ion batteries. One caught fire at Boston's Logan airport.
The aircraft resumed flying in May after Boeing made redesigns to the battery system that were approved by global aviation regulators.
Ethiopian Airlines, whose Dreamliner caught fire at Heathrow on Friday, was the first operator to resume flights of the 787.