25 Boeing 737 MAX 9s To Be Inspected For Missing Fuel Sealant

An issue with work instructions caused 25 Boeing 737 MAX 9 jets to be shipped off to their new owners without fuel sealant between April 2018 and February 2019. The FAA is now proposing an airworthiness directive that would make it mandatory for operators to inspect the jets in question. Failure to address the problem, it says, could result in large ground fires.

Boeing 737 MAX 9
The FAA is proposing an inspection of 25 Boeing 737 MAX 9 aircraft. Photo: Boeing

The MAX – FAA saga not quite over

While the 737 MAX is making an incremental comeback tour, woes over some specific aircraft of the model are not quite done. According to a proposed airworthiness directive (AD) released on January 19th, the Federal Aviation Administration (FAA) is recommending inspections of 25 Boeing 737 MAX-9s in accordance with a service bulletin Boeing issued in April last year.

The regulatory body says it determined that a fuel sealant had not been applied during the planes’ manufacturing. The sealant is supposed to act as a fuel barrier on blow-out doors to prevent fires.

“Application of sealant on the left wing and right wing leading-edge outboard blowout door was missing during the airplane manufacturing process on some model 737-9 airplanes,” says the proposed order, which has been seen by FlightGlobal. 

“In the event of a substantial fuel leak from the wing box, missing sealant could result in an unintended drain path allowing fuel to come into contact with the engine,” the order reads. The FAA further stated that this could result in a “large ground fire.”

United MAX 9 taking off
Most of the MAX 9’s that require inspection are in United Airlines’ fleet. Photo: United Airlines

Stay informed: Sign up for our daily aviation news digest.

Boeing issued instructions to operators last spring

The FAA is proposing that operators be required to perform actions that Boeing has outlined in a service bulletin the manufacturer issued regarding the matter in April last year.

“We notified operators of this issue in April 2020. At that time, we provided detailed instructions on where to inspect and how to apply the sealant if it was missing,” Boeing said in a statement shared with Simple Flying. “We fully support the FAA’s action to make our recommendations and instructions mandatory.”

The planemaker says it recommended that carriers with the affected aircraft in their fleet should resolve the matter within 12 months. Meanwhile, the exact time frame will now be set by the FAA directive. The issue with the missing sealant itself stemmed from work instructions, which have since been updated.

Copa Airlines 737 MAX 9
Six of the jets in question are with Copa Airlines. Photo: airbus777 via Wikimedia Commons

Most of the jets with United

Fourteen of the MAX 9 jets in question are with United Airlines. The remaining are spread all over the world. Copa Airlines, which resumed operations with the type just before the new year, has six. FlyDubai has three, and Icelandair and Turkish Airlines have one, respectively. All of the planes were delivered from April 2018 to February 2019.

United has 25 MAX 9 aircraft in its fleet, six of which have been brought out of storage since the model’s ungrounding by the FAA in November last year. The airline has another 163 of the MAX on order. One hundred are for the 737 MAX 10, and the remaining for more MAX 9s. The carrier is set to resume revenue flights with the MAX in February.

What do you make of the case of the MAX 9 missing fuel sealant? Let us know your thoughts in the comments.