An unresolved software flaw won’t delay the first delivery of the Boeing KC-46A tanker after the US Federal Aviation Administration approved a temporary exemption from safety requirements.

Boeing’s engineers discovered earlier this year that the KC-46A lacks an independent system to monitor fuel flow, as required by the FAA’s safety regulations.

If a single processor fails while the KC-46A is receiving fuel from another tanker, an overpressure event in the centre fuel tank may go undetected, according to Boeing’s nearly four-month old request for a temporary exemption.

On 2 August, the FAA approved Boeing’s exemption from the safety requirement, allowing the aircraft to be used on operational flights as scheduled after October.

The FAA’s approval requires the USAF to operate the KC-46A in domestic airspace with another crew member in the cockpit to physically monitor the pressure in the centre fuel tank during an in-flight refueling.

The exemption expires on 30 June, but Boeing plans to release a new software update that fixes the problem by then, the FAA says.

In late June, Boeing announced that the USAF has agreed to accept the first KC-46A tanker more than a year late in October. Boeing has reported more than $3 billion in financial charges related to the programme since winning the development contract in 2011.