Pratt & Whitney’s service instructions used as the basis for an FAA mandatory near-term inspection order on certain PW1100G turbofans provide little insight into the checks beyond a list of affected engines and uninstalled disks.

The Aug. 4 “special instruction (SI)” bulletin that the FAA used as the basis for its Aug. 22 airworthiness directive lists 201 engines by serial number believed to have high pressure turbine (HPT) stage 1 and stage 2 disks, or hubs, in the affected population of suspect parts. Within that population were 55 engines Pratt data shows as being off wing, including spares and units in overhaul shops. Several engines have multiple disks flagged in the affected population.

Another 80 disks were not linked to specific engines, suggesting they are spare parts or have already been removed. 

The exact number and breakdown of affected engines in the global fleet has not been previously reported.

Pratt’s bulletin recommends removing affected engines from service by Sept. 15 and conducting checks, which must be done off-wing. The FAA directive, also adopted by the European Union Aviation Safety Agency (EASA), gives affected operators until Sept. 28. 

“Review of production records identified a limited number of HPT stage 1 and stage 2 hubs which, based on Time of Flight (TOF) records review, are required to be scanned using angle ultrasonic scan inspection (AUSI) to determine serviceability as prescribed in this SI,” the bulletin said. 

Affected engines were made from late 2015 through early 2021, Pratt determined. They contain potentially contaminated powder metal (PM) supplied by HMI Metal Powders, which like Pratt is part of RTX, formerly Raytheon Technologies. Contamination makes the disks susceptible to cracking. 

The initial set of engines flagged for checks includes 20 on U.S.-registered aircraft, the FAA said.

Pratt has not detailed which operators are affected. 

An Aviation Week analysis shows more than 900 Pratt-powered Airbus A320neo-family aircraft were rolled out in the time frame that matches when the suspect engines were made and delivered to Airbus. India’s IndiGo operates the most by far, with 135. Five other carriers—Air China, Go First, Lufthansa, Spirit Airlines and Volaris—each have at least 40.

Neither Pratt’s bulletin nor FAA’s order detail what if any engine-specific in-service time metrics the engine-maker used to flag the initial set of disks.

Aviation Week data show that the 100 highest-time Pratt-powered A320neos delivered within the time frame flagged by Pratt have between 15,000-20,000 total flight hr. (FH). Some of these aircraft likely have different engines than the ones they entered service with, however. Durability problems that have plagued the fleet mean many PW1100GS have been removed, repaired, and re-installed on different airframes than the ones they were delivered on as operators seek to keep as many of their new narrowbodies flying as possible.

The initial set of 201 engines flagged for immediate inspections have at least one of about 400 of the potentially contaminated PW1100G disks, Pratt’s records show. The disks are part of a larger subset of nearly 2,100 disks identified as being made during the time frame when PM contamination was suspected. 

Another subset of disks in about 1,000 engines is expected to need inspections within the next 12 months, RTX said in July while revealing its updated recommendations. Pratt identified the full population of disks in 2022 and recommended they be inspected during scheduled shop visits. An FAA AD issued in October 2022 mandated the checks, noting that 189 engines on U.S.-registered aircraft would be affected.

A December 2022 incident unrelated to the HPT disks and revealed in the latest FAA directive prompted Pratt to take a broader look at its risk analysis process. Among its conclusions: inspections of the highest time PW1100G HPT disks under scrutiny could not wait until scheduled overhauls.

So far, the only in-service aircraft affected are PW1100G-powered A320neo variants. Pratt is analyzing PW1500G and PW1900G records to determine the ramifications for the A220 and Embraer E2 fleets. The Pratt bulletin does not reference either engine variant. 

Pratt, through RTX, declined to answer Aviation Week’s inquiries.