Russian officials have announced they may suspend the Boeing 737’s airworthiness certificates.

A recent report by Sputnik suggests the Russian Federal Agency for Air Transport (Rosaviatsiya) may ban Russian airlines from flying Boeing Co’s (NYSE:BA) 737 aircraft, owing to safety concerns.

An appeal to cancel the Boeing 737’s flying certificate was sent by Russian Civic Chamber committee chairman, Artyom Kiryanov, to Rosaviatsiya head Alexander Neradko, as well as Interstate Aviation Committee (IAC) chair Tatiana Anodina. Russian officials expressed concern over the plane model after the recent Flydubai 737 crash in Southern Russia.

The appeal has called upon regulatory officials to work with the International Air Transport Association (IATA) and Boeing, to make sure that the company and its aircraft meet safety standards. The company has also been asked to present technical details of the plane, particularly information related to its rudders.

The IAC had previously requested for Boeing 737s not to be used in November, following an investigation into the same model’s rudder systems. This was after a 737 part of the fleet of Russian carrier Tatarstan Airlines, crashed in 2013.

Russian airlines operate more than 190 units of the 737 across the country, and most of them are used for local flights. Currently, the country has about 64 orders of new 737 aircraft pending, of which 40 are still to be delivered.

The Crash

Flydubai’s FZ981 is reported to have been circling Russia’s Rostov-on-Don airport on March 19 for more than two hours, due to severe weather conditions, high-level winds, and low visibility.

The plane attempted to land twice, and the second one proved to be lethal. The plane crashed near the airport leaving 55 passengers and 7 crew members dead. This was the airline’s first crash, and the reason for it is still unknown.

Flydubai will continue flying the 737

Flydubai has announced that it has no plans to reconsider its orders for new Boeing planes.

A Flydubai spokesman said: “We have no intention to reconsider the new aircraft order with Boeing and we remain confident in our fleet.”

The airline carrier has a fleet of 50 next-generation 737-800s, and is expected to accept deliveries of more than a 100 new Boeing planes by 2023.

Boeing is currently gathering information to arrive at a conclusion as to what went wrong. It has already recovered memory from the aircraft’s black-box, but Boeing says the decoding process could take several weeks or months.

Recent Safety Check Concluded Plane Was Fit

The Flydubai FZ981 aircraft had a major C-check in January this year, and was found fully fit to function. The plane was only 5 years old, and was part of Boeing’s next-generation 737-800 aircraft fleet.

The 737s are seen as one of the safest planes ever made, and Boeing has said the plane is its highest selling model. Needless to say, none of these things would be true if the plane had radical safety shortcomings.

Early reports suggest the aircraft had circled the runway for over two hours, before making its first landing attempt. A mechanical problem would have prevented it from that.

Transitioning to 737-MAX

As Boeing undergoes a transition phase with the 737s, a cancellation of its airworthiness certificates may have a severe impact on the company. Boeing is giving substantial attention to the shift, and expects the model’s deliveries to take place in the second half of 2017.

If the requests for the cancellation of Boeing’s flying license is approved, Russian carriers may return their Boeing planes, which is the last thing its transition program needs. The company is already trying to desperately get rid of the older versions of the 737.