The Irish low-cost carrier Ryanair has warned the delivery of its Boeing Max aircraft could face further delays.
The company has reported an unchanged net profit of €1.15bn for the first half of the year.
It says while traffic grew by 11% to 86 million passengers, its revenue per passengers rose by 1%.
It comes after the airline launched a new environmental policy in September.
It is committing to be plastic free in five years, cut noise emissions by up to 40% per seat and to cut CO2 emissions by a further 10% by 2030.
However it says the delivery of its first Boeing 737-MAX-200 aircraft has been "repeatedly delayed" from the second quarter of the year.
The US aircraft-maker ground its entire 737 Max fleet in March, after two crashes involving that model of aircraft.
Earlier that month, 157 people died - including Irish engineer Micheál Ryan - when an Ethiopian Airlines plane came down shortly after take-off from Addis Ababa.
That came five months after a Lion Air flight crashed shortly after take-off from Jakarta, killing all 189 people on board.
A Ryanair statement says: "We now expect our first Max aircraft to deliver in March/April 2020 at the earliest", subject to European Union Aviation Safety Agency (EASA) approval.
"The risk of further delay is rising", the carrier warns.
It adds that it expects to receive only 20 MAX-200s - rather than 58 as previously thought - around the middle of next year.
This has seen it cuts its growth rate from 7% to 3%.
But the airline says: "We remain confident that these 'gamechanger' aircraft... when delivered will transform our cost base and our business for the next decade.
"Due to these delivery delays, we will not see any of these expected cost savings delivered until FY21."
In terms of outlook, Ryanair says it "remains cautious" for the rest of this year.
It expects full year traffic will grow 8% to 153 million passengers - but also expects a "slightly better" fare environment than last winter.
However it adds that this "remains sensitive to any market uncertainty", such as a no-deal Brexit.
It also says that losses at its Austrian low-cost airline Lauda will be "higher than originally expected".