The flight data analyst compared airlines’ planned 737 Max capacity prior to the worldwide grounding in March with the current schedules filed for all Max operators.

OAG found scheduled capacity as of 18 February, a month before a second fatal crash involving the 737 Max, stood at about 62.7 million seats.

Schedules filed as of 5 August showed scheduled 737 Max capacity had shrunk by almost two-thirds – 41 million seats – to just shy of 21.4 million.

In a blog post, OAG senior analyst John Grant described the discrepancy as “staggering” and estimated the likely effect of lost capacity, based on the Max returning to service in November and a “notional” cost of $100 per seat, “could run towards” some $4 billion.

A number of US carriers have already pushed their 737 Max schedules back to November, but there is yet no guarantee the aircraft will be able to return to service this year.

The 737 Max was grounded in March following a second fatal crash in just five months when Ethiopian Airlines flight 302 came down en route to Nairobi, killing all 157 people onboard.

Last October, Lion Air flight 610 crashed in the Java Sea shortly after taking off from Jakarta. All 189 people onboard were killed.

Preliminary investigations into both crashes suggest the same deep-seated control system was active when both aircraft crashed.

Boeing is working on a software fix, additional safety systems, and new pilot training. However, these are yet to be submitted for the US Federal Aviation Administration for approval.

While significant capacity has been lost in North America where a number of US carriers have been using the 737 Max to operate domestic routes, there has been a severe impact in Europe too.

Norwegian Air Shuttle is down 2.17 million seats (63%), Lot Polish Airlines down 1.97 million (85%), Tui Airways down 900,000 (63%) and Icelandair down 1.10 million (75%).

China Southern has been hardest hit with the loss of 3.8 million seats.

“The scale of the 737 Max grounding has been very disruptive for many,” said Grant, who added the switch during the last week of October to airlines’ winter schedules was an added dilemma.

“That date is a key planning milestone for many carriers and at the moment, a number of airlines continue to show 737 Max services from the end of October as they are yet to finalise and adjust their schedules,” he said.