The US National Transportation Safety Board (NTSB) has released its preliminary report into the serious incident involving a Boeing 737-800 that suffered a failure of its right-hand engine on July 10 while flying from Thessaloniki to Memmingen. Engine debris struck the fuselage and shattered a passenger window. Investigators have highlighted two particularly significant findings: bird remains were found inside the damaged engine, while the same engine had been involved in four other reported suspected bird strikes during the previous 12 months. At the same time, clear evidence of fatigue damage was found on the fractured fan blade. The NTSB has not yet determined whether there is a causal link between a bird strike and the blade failure.

The aircraft, registered 9H-QEU and operated by Malta Air on behalf of Ryanair, was performing flight FR1879 from Thessaloniki to Memmingen, Germany. While climbing through approximately 16,000 feet near Polykastro, the crew received an indication of high vibration from the right-hand CFM International CFM56-7B26 engine. Engine power was reduced and the vibration temporarily decreased, allowing the crew to continue the climb.

Shortly afterwards, however, the vibrations increased sharply and a loud bang was heard. The autopilot disconnected and a cabin altitude warning was triggered almost simultaneously. The pilots donned oxygen masks, declared an emergency and initiated an emergency descent.

Engine debris struck the right side of the aircraft, including the fuselage and right horizontal stabilizer. The pressurized fuselage was punctured in two locations, while one fragment struck and completely shattered a window in Row 11.

The passenger seated in 11F was partially pulled into the window opening before other passengers managed to pull him back into the cabin. He sustained serious injuries. There were two pilots, four cabin crew members and 149 passengers on board, including one lap infant. After descending below 10,000 feet, the pilots shut down the right engine and returned safely to Thessaloniki.

Inspection of the engine showed that fan blade No. 10 had fractured below its platform, while the tips of blades No. 16 and 21 had also broken off. The remaining blades retained their full length but showed varying degrees of impact deformation. Three loose blade fragments were also recovered from the engine.

Investigators found no evidence that fragments had penetrated radially through the engine case or that a fire had occurred beneath the cowling, although the engine inlet sustained significant damage.

Of particular interest is the metallurgical examination of the fractured blade. According to the NTSB, blade No. 10 fractured through its dovetail, with approximately 37% of the total fracture surface displaying characteristics of fatigue cracking. The crack originated on the concave side of the blade near the trailing edge, next to an area of pronounced contact wear on the adjoining dovetail surface.

Scanning electron microscope examination revealed features consistent with High Amplitude Fatigue (HAF).

This is an important finding because the preliminary report does not simply attribute the event to a bird strike. At the same time, investigators found bird remains, including feathers, at several locations within the right engine, including the integrated drive generator oil cooler, a thrust reverser component and the lower section of the fan case. Samples were sent to the Smithsonian Institution’s Feather Identification Laboratory in Washington for identification and further analysis.

Maintenance records revealed another notable detail. During the 12 months preceding the accident, crews reported four suspected bird strikes involving the same right-hand engine. Inspections following those events found no damage, although bird remains were discovered after two of them.

If the remains found following the July 10 event are confirmed to have resulted from another bird strike, this would represent the fifth such event involving the same engine in approximately one year. However, at this stage the NTSB has not concluded that a bird strike caused the fan blade to fracture.

The fan blades had also been subject to the prescribed inspection programme. According to the NTSB, they underwent ultrasonic inspections on November 11, 2025, and again on May 24, 2026, just 253 cycles before the accident. No defects were reported during either inspection.

The inspections were performed in accordance with a CFM service bulletin requiring periodic ultrasonic examination of the blade dovetail area specifically to detect developing cracks.

The programme is closely linked to previous serious CFM56-7B fan blade failures. In April 2018, a Boeing 737-700 operating Southwest Airlines Flight 1380 suffered a fan blade fracture caused by metal fatigue. Engine cowling debris struck the fuselage, shattered a passenger window and caused rapid decompression. One passenger was killed.

The NTSB determined that the probable cause of that accident was a low-cycle fatigue crack in the fan blade dovetail. A similar failure occurred on Southwest Airlines Flight 3472 in 2016, when debris also damaged the fuselage and caused depressurization, although nobody was injured.

Following those incidents, the FAA mandated additional modifications to Boeing 737 Next Generation aircraft aimed at reducing the consequences of future fan blade failures. Airworthiness Directive AD 2025-04-01, for example, requires modifications to engine inlet structures and attachment points designed to reduce the likelihood of inlet debris separating and striking the fuselage or passenger windows following a blade failure.

The FAA explicitly identified such a scenario as a potential hazard to passengers seated next to windows behind the wing.

The NTSB found that aircraft 9H-QEU had not yet incorporated certain modifications required by AD 2025-04-01, 2025-04-02 and 2025-04-03, covering the engine inlet, fan cowling and exhaust nozzle.

This did not mean the aircraft was operating outside regulatory requirements, as operators have until July 2028 to complete the modifications. The preliminary report also does not conclude that the absence of these modifications contributed to the accident.

The similarities with Southwest Flight 1380 are therefore evident in the sequence of consequences — a fan blade fracture, damage to structures surrounding the engine, debris striking the fuselage, a shattered passenger window and rapid decompression — but the underlying cause may not be the same.

In the Southwest accident, investigators identified low-cycle fatigue, while the blade from the Ryanair/Malta Air aircraft has preliminarily shown evidence of high-amplitude fatigue, together with evidence of bird material inside the engine. Investigators are examining potential similarities with previous events, but no final conclusions have yet been reached.

The investigation remains ongoing, with key questions including the origin of the bird remains, the development of the fatigue crack in the fan blade and whether there is any relationship between the two findings. Investigators are also analysing flight and cockpit voice recorder data, the engine and its components, and the structure surrounding the Row 11 window.

The NTSB stressed that the report is preliminary and that its findings may change as the investigation progresses.