Boeing only received orders for four new planes in May as it continues to deal with safety concerns blowback

Boeing reported just four aircraft orders last month as concerns rise over safety processes at the major aerospace company.

These low order numbers come as Boeing faces ongoing safety concerns and federal investigations, with dozens of whistleblowers hoping to share their worries about the quality of the company’s products. The latest sales figures were released on Tuesday.

Boeing, with its four orders in May, also delivered 24 jetliners to buyers last month, the Associated Press reports. Meanwhile, its competitor Airbus made 53 deliveries. Airbus also had 27 orders for new planes in May, but 12 have been canceled, for a net of 15 new orders.

Boeing also received zero orders for the 737 Max for the second month in a row, despite its previous status as a best-seller.

Boeing still has a backlog of more than 5,600 orders, the AP reports, and is facing criticism from buyers around the world waiting on their planes.

Boeing safety concerns first made national headlines when a doorplug blew out a Boeing plane mid-flight in January. While there were no major injuries, passengers were left shaken following the emergency landing. Three of those on board sued the airline.

That sparked a federal investigation into the manufacturer’s safety record in building plans. Since that event, Boeing has been hit by several high-profile incidents of troubles in the sky or on the ground, sparking safety concerns. Federal investigators are now conducting both criminal and civil investigations into the airline.

Several employees have also spoken out over concerns with safety at Boeing.

Sam Salehpour, a current quality engineer for the manufacturer, told a congressional committee in April that Boeing has a “culture of retaliation” when employees speak up about their concerns.

When asked if the planes are safe, Salehpour testified: “It’s like an earthquake. When that hits the building … [it has] to be prepared to accommodate that type of shake-up… Right now, from what I’ve seen, the airplanes are not being billed per spec, and per…