The United Kingdom has banned American made Boeing 737 Max planes from operating in or over its airspace, following a second fatal crash involving the plane in less than five months.

The move leaves US regulators, airlines and the manufacturer increasingly isolated in maintaining the plane is safe.

A spokesman for the UK civil aviation authority said: “As we do not currently have sufficient information from the flight data recorder [black box] we have, as a precautionary measure, issued instructions to stop any commercial passenger flights from any operator arriving, departing or overflying UK airspace.”

British pilots’ union Balpa welcomed the decision, saying: “Safety must come first.”

Two Turkish 737 planes headed to Britain appear to have been forced to turn back to Istanbul in midair, according to FlightRadar24.

TUI, the world’s largest travel and tourism company, said it would discontinue using the 737 Max across all six airlines in its group.

On Tuesday, Australia and Singapore suspended operations of all Boeing 737 Max aircraft in and out of their airports, after Indonesia and China grounded their fleets of the Boeing 737 Max 8. Oman and South Korea have also followed suit.

The Zimbabwe Government advised citizens to check that they were not booked into 737s before boarding any flight warning that the American plane is not safe.