The Boeing 737 Max could be grounded until the new year as fixes to the aircraft at the centre of two crashes are yet to satisfy all safety requirements, officials and union leaders have claimed.

A software problem is understood to have been fixed months ago, but regulators at the US Federal Aviation Administration and pilot union leaders have told The Wall Street Journal that the list of issues for Boeing to work on has continued to grow.

All fixes will need approval from the FAA and further delays could result when the body appoints Stephen Dickson, a former Delta Air Lines executive, as its new administrator in the autumn.

Podcast: Is the aviation sector in turmoil?

American Airlines said yesterday that 737 Max cancellations had been extended until November 2 – its previous target for the resumption of services had been September. The latest move means that 115 flights a day will be cancelled and other services will be covered using substitute aircraft.

United Airlines was meant to have 16 more of the new generation in its fleet in the coming months, but has had to cut 2,900 flights in October because of the postponement of their delivery.

American Airlines said it “remains confident that impending software updates to the Boeing 737 Max, along with the new training elements Boeing is developing in co-ordination with our union partners, will lead to re-certification of the aircraft this year.

“We are in continuous contact with the Federal Aviation Administration (FAA), Department of Transportation (DOT), National Transportation Safety Board (NTSB) and other regulatory authorities.”

Boeing told the WSJ it intends to “provide the FAA and the global regulators whatever information they need”, adding that the company would not offer the 737 Max for certification “until we have satisfied all requirements”.

The process of developing and certifying new software, then training pilots to use it, has been delayed repeatedly, with airlines struggling to cope with frequent revisions to the timetable during the exceptionally busy summer, The Times reported.

A total of 346 people were killed in two 737 Max crashes operated by Lion Air in Indonesia and Ethiopian Airlines in Ethiopia in less than six months leading to the worldwide grounding of the type in March.

Passengers have had to rebook journeys, pilots and cabin crews have had to be reshuffled and airlines have been forced to cancel flights.

MoreSpecial Report: Boeing MAX-ed out by disasters

British family starts legal action over Boeing 737 Max crash

Boeing pledges $100m to 737 Max crash victims