Date: 202106
Local time of day: 0001-0600
Location: ZZZ.Airport, US
Aircraft: B737-800
Operator: Air Carrier
Operating under: Part 121
Mission: Passenger
Flight phase: Parked
Aircraft component: Engine
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Technician
Reporter qualification: Maintenance Powerplant; Maintenance Airframe
Human factors: Troubleshooting
Second reporter function: Technician
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Overcame Equipment Problem; General Flight Cancelled / Delayed; General Maintenance Action
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: Aircraft X had a dual engine wash on the night of Date. Maintenance Technician 1 and I performed the run up after engine wash; followed Job Card XXX-XX-XX. Taxi aircraft onto taxiway for run up to 60%; 60% run was not done at the blast fence as paperwork doesn't specify location. At 60% run up and operation of packs system no smell/odor was detected in the flight deck or in the cabin. So we proceeded with the Job Card and finished the aircraft. Following day Aircraft X was taken out of service after a flight to ZZZ1 with crew report smell/odor in cabin. This was the first of 2 aircraft we had engine washes on that evening (both 800s); other aircraft Job Card complied with same was as we did Aircraft X- on taxiway same parameters met. The 'smell/odor' seems to be a common problem with the 800 as the Job Card does not state how long to actually run at 60% just to 'packs operate until the air that goes into the control cabin...no smell of the oil contamination'. The 700 has a different Job Card time requirement and seems to have less issues with 'smell/odor'. Cause of flight crew 'smell/odor' discovery may be out of Maintenance Technician's control as engines and packs have been run longer and at different altitudes/temperatures/parameters. Have the Job Card for the 700/800/MAX mirror each other so all aircraft and all technicians are performing job the same way to avoid  gate return/air returns/out of service aircraft.


Second narrative: Aircraft X was taken out of service in ZZZ1 for oil smell after it landed there from ZZZ after having performed an engine compressor wash. Flight crew reported it. My co-worker and I believe we followed the Job Card and hit the times and parameters that it asks for. Maintenance Technician 2 and myself did not smell anything; this could be due to becoming acclimated. The company pointed out that we needed to be at the blast fence for the 60% N1. I was unaware of this. The task card does not specify to do so. As it only requires a very short time at 60% we set brakes during taxi to run the engine up. We also did an engine compressor wash on another 800 aircraft the same shift the exact same way. Only Aircraft X was taken out of service. This leads me to think that maybe something else may have caused the oil smell. Also after talking to other employees about this; I hear there have been multiple similar situation of 700 series aircraft going out of service following engine compressor washes. So much so that the company has changed the Job Card for the 700 series engine compressor washes. They run the engine at 60% N1 much longer. Why the 800 does not mirror the 700 Job Card is unknown.


Synopsis: Aviation Maintenance Technician reported being notified of aircraft removed from service due to a fume event the day after they performed dual engine wash.