LONDON (TIP): British aviation investigators identified an emergency beacon made by Honeywell International Inc as a likely source of last week’s blaze on a Boeing Co 787 Dreamliner and called for it to be turned off, spurring a rally in Boeing shares by relieved investors. The Air Accidents Investigation Branch (AAIB) said the locator beacon and its battery was the only system on a parked Ethiopian Airlines plane at Heathrow that was near the fire and had the power to start it.

Boeing said the beacon could be removed in about an hour from its newest model plane, which was grounded for more than three months earlier this year because of overheating of lithium-ion backup batteries in two January incidents. Shares of Boeing closed 2.7% higher at $107.63, near the high of $108.15 reached a week ago before the fire. The AAIB said it remained unclear whether the fire was triggered by a malfunction in the beacon’s lithium-manganese battery or some external force – such as an electrical short circuit – and said the probe would continue.

In its report, the AAIB also called on theUS Federal Aviation Administration and other regulators to review use of such emergency beacons that use lithium-based batteries on all other aircraft. UK officials said last week’s fire was unrelated to the January incidents that grounded the 787. Investigators never determined what prompted the batteries involved in those cases to melt down, but Boeing resolved the issue by fireproofing the box they come in, and finding a way to vent any possible fire outside the plane.

While the UK report focused on the beacon made byUS conglomerate Honeywell, aviation experts said there could also be issues with the 787’s higher humidity or other environmental factors. Water can conduct electricity, so high moisture levels could increase the likelihood of short circuits. “The investigators are looking at everything, humidity, condensation and … how things are installed. It’s a comprehensive effort,” said one industry source.