Boeing's newest plane will face much heavier scrutiny with European aviation regulators less willing to rely on American authorities approving the jet.
The European Union Aviation Safety Agency (EASA) said it will perform a "concurrent validation" of Boeing's 777X, an upgraded version of the existing wide-body plane expected to enter service in 2021.
This means that instead of largely relying on the Federal Aviation Authority's (FAA) sign-off on the new aircraft as airworthy and effectively rubber-stamping its approval, EASA will conduct its own checks.
This is a break with modern practice, with EASA largely relying on the FAA to approve US-designed aircraft, and vice-versa for Airbus planes.
EASA said that the decision came in the wake of two crashes suffered by Boeing's 737 Max planes killing 346 people.
The European regulator said: "Following the lessons learned from the ongoing review of the 737 Max, we have adjusted our level of involvement."
However, EASA added the change was "in line" with the existing regime, with its involvement limited to areas where it has different regulations to the US, unusual or novel designs, new methods of meeting regulations or "sensitive issues usually associated with an accident or incident".
The 777X faces further pressure, with the Wall Street Journal reporting a similar move by the United Arab Emirates' aviation authority which will also scrutinise the new aircraft. The Gulf state's Emirates airline is expected to be the first to fly the 777X.
Boeing said: "We remain fully focused on safety as our highest priority as we subject the 777X to a rigorous test programme."
The news came as the FAA said its own staff will now check every new 737 Max is fit to fly in the wake of crashes, stripping Boeing of the ability to do so itself.
The FAA will in future issue an airworthiness certificate for each new jet. Previously, Boeing was able to issue its own certificates.
The two 737 Max crashes which resulted in the fleet being grounded in March are believed to be related to glitches in systems intended to make the aircraft safer by preventing stalls.
Although the 737 Max cannot be flown until the cause of the crashes is determined and a fix implemented and certified, Boeing is still producing the aircraft at its plant near Seattle.
US politicians labelled the jets as "flying coffins" last month as they grilled Boeing boss Dennis Muilenburg about the crashes and the company's knowledge of problems with the Max before the crashes.
The FAA said that once the 737 Max has been cleared to fly again, only the FAA will be able to issue certificates for each new plane produced.
Regulators said that 737 Max planes already delivered to airlines will not be affected by the change, although these will have to meet all FAA requirements.
Boeing said: "We continue to work with the FAA on the safe return to service for the Max.”
The company is piling up undelivered aircraft at its plant, forcing some to be stored in staff car parks. An estimated 350 jets which cannot be handed over to customers will have been produced by the end of the year.
Some airlines with the 737 Max in their fleets cancelled flights into January and February because of the grounding. The FAA is not expected to the aircraft's return to the skies until December at the earliest. European airline Ryanair is among those affected.
Robert Stallard, analyst at Vertical Research Partners, believes the Max will not be back in service until at least March 2020, forcing Boeing to pay even more compensation from airlines.