In a statement, the aviation regulator said operators “are encouraged to conduct a visual inspection to ensure the door plug is restrained from any movements”.
The FAA said some airlines had conducted additional inspections on the 737-900ER mid-cabin exit door plugs and had noted “findings with bolts during the maintenance inspections”.
Regulators have stepped up scrutiny on Boeing after a cabin panel flew off mid-air during an Alaska Airlines Max 9 flight on January 5, leaving a gaping hole in the aircraft fuselage and forcing an emergency landing.
Boeing has been scrambling to contain the fallout from the Alaska incident. It has brought in a retired Navy admiral, Kirkland H Donald, to review its quality management systems. Important customers, including Ryanair and aircraft lessor AerCap, have in recent weeks warned that the company needs to focus on safety and quality control.
According to Boeing data, more than 500 of the 737-900ER models have been delivered to airlines globally. Leading operators include United Airlines, Alaska Airlines and Delta Air Lines. The three US carriers fly the majority of the 380 aircraft understood to have the door plug affected by the recommendation.
The FAA grounded 171 Boeing 737 Max 9 planes after the incident. Last week, the FAA said inspections of an initial group of 40 Boeing 737 Max 9 jets had been completed, a key hurdle to ending the grounding of the model.
United said it started “proactive inspections” of its Boeing 737-900ER jets last week and expected to complete them “in the next few days” without disruption to travellers. The Chicago-based carrier has 136 Boeing 737-900ER aircraft in its fleet.
Alaska said it began inspections of its 737-900ER aircraft “several days ago”. It had “no findings to date” and did not expect disruption to its operations.
Delta said it also “elected to take proactive measures to inspect our 737-900ER fleet” and it did not expect “any operational impact”.
“We remain in close communication with the Boeing team,” the Atlanta-based airline added.
The door plugs replace mid-cabin emergency exit doors and are installed depending on the configuration used by the respective airline operator. They are common features and have been used on both Boeing and Airbus aircraft for decades.
A Boeing spokesperson said: “We fully support the FAA and our customers in this action.”
The 737-900ER is more widely used than the 737 Max 9. It is an older model but has the same optional door plug design that allows for the addition of an extra emergency exit door when carriers opt to install more seats.
There are 490 Boeing 737-900ER jets in service, at least 79 of which have an active door rather than the plug because they are operated by low-cost airlines with denser cabins, according to Cirium data.
The chief executive of United Airlines, one of Boeing’s biggest customers, has increased the pressure on the manufacturer, warning he is rethinking a big order for new aircraft.
Scott Kirby on Tuesday said he was “disappointed” with the ongoing problems at Boeing, and called for it to take “real action”.
“I am disappointed that the manufacturing challenges do keep happening at Boeing, this isn’t new,” he said in an interview with CNBC. “They need to take action...it needs to be real action,” he said.
Kirby said the groundings meant United was rethinking a large order for the newer, larger Max 10 aircraft, production of which is running years behind and has yet to be certified by regulators.
“I think the Max 9 grounding is probably the straw that broke the camel’s back for us. We will at least build a plan that doesn’t have the Max 10 in it,” he said. United has agreed a multibillion-dollar order for 277 of the Max 10, with options for another 200.
Kirby’s frustration came as United said it expected to take a financial hit from the groundings in the first quarter, and that its longer-term growth plans would be hit by Boeing delivery delays.
“We are not going to grow quite as fast as we otherwise would have, because the reality is Boeing isn’t going to be able to deliver us all the aeroplanes in the [promised] timeframe,” he said.
Kirby’s comments represented some of the most significant criticism of Boeing since the crisis began earlier this month.
He said the order was not cancelled. Kirby would not be drawn on where else United would find planes to meet its ambitious growth plans. He did not say whether he had engaged in discussions with Boeing rival Airbus over a replacement order.
Speaking on United’s earnings call on Tuesday, chief financial officer Michael Leskinen said it was “unrealistic” to expect the full compliment of 31 Max 9 deliveries from Boeing this year, and that delays from the plane maker more broadly could be expected into 2025.
As Boeing scrambled to limit the reputational damage from the Max 9 grounding, which has come amid wider delivery delays, one of its most senior executives issued an apology to the affected airlines.
“We have let down our airline customers and are deeply sorry for the significant disruption to them, their employees and their passengers,” Stan Deal, president and chief executive of Boeing Commercial Airplanes said.
Despite the financial impact from the Boeing groundings, United’s shares rose nearly 7% on Tuesday after it reported fourth-quarter results that beat forecasts, highlighting its “busiest travel period in history” in late December. It reported net income of $1.81 a share on $13.6bn in revenue in the three months ended December 31, topping consensus estimates on both measures.
Boeing cannot “afford another slip-up” with its 737 Max family of aircraft and must set aside financial targets to focus solely on quality and safety, the head of one of the world’s largest aircraft owners has warned.
“Given what has happened with the two fatal crashes and this incident, the financial targets have to take a back seat for Boeing and its supply chain,” said Aengus Kelly, chief executive of the world’s biggest aircraft leasing company AerCap, in a media interview.
“Boeing must now focus 100% on quality and safety metrics. Financial metrics are completely secondary to the future of the company at this point.”
Michael O’Leary, chief executive of Ryanair and one of the biggest buyers of the aircraft, said last week that the airline has doubled the number of its engineers overseeing Boeing’s production lines.
