Grounded Boeing 737 Max aircraft could be out of service for months until a software update can be tested and installed.
The aircraft would be banned from flying for weeks at a minimum, the US aviation regulator revealed.
However, the grounding could be longer after the second crash involving the new model in five months.
US Federal Aviation Administration acting head Dan Elwell was briefing US congressmen following the Ethiopian Airlines disaster on Sunday which killed all 157 people on board.
This followed a fatal Lion Air Max 8 crash in Indonesia last October.
More: Tui vows to maintain flying programme as UK grounds 737 Max
Norwegian to bill Boeing for 737 Max disruption
Nine Britons now confirmed dead in Ethiopian Airlines crash
The FAA said on Wednesday that a software fix for the Boeing 737 Max that the US manufacturer had been working on since the Lion Air disaster would take months to complete.
Two black flight recorder boxes from the Ethiopian Airlines crash arrived in Paris yesterday to be analysed.
The grounding the 360 Max aircraft in service will be felt mostly in the US and Asia, although Tui Airways has five of the new aircraft and Ryanair is about to receive the first of a major order for the new 737 variant.
Russia, Japan and Tunisia became the latest countries to ban the aircraft from their airspace following action by the UK Civil Aviation Authority and other regulators.
Tui confirmed on Wednesday that holidaymakers due to fly on Max 8 aircraft in the coming days will travel as planned on other aircraft.
However, Tui Airways warned today of delays of up to four hours on flights from Manchester to Las Palmas and Birmingham to Hurghada without explaining the reason.
