B737 MAX 9
Troubleshooting; Situational Awareness; Confusion
Ground Event / Encounter Ground Equipment Issue
Flight Crew Became Reoriented
Equipment / Tooling; Aircraft; Human Factors; Procedure
The Lead was marshalling in the flight and stopped it short of the 737-900MAX stop line. We attached the wrong tow bar to a 737-900MAX upon seeing that we attached the wrong tow bar we stopped and disconnected the tow bar. Thinking that the brakes were set; the 737-900MAX rolled back a couple of feet. We froze the scene and called for the supervisor. No one was hurt or any damage to the aircraft. After the supervisor looked at the scene; took pictures and saw that no one was hurt and there wasn't any damage to the aircraft we hooked up the correct tow bar and proceeded to pull the aircraft back in a couple of feet to the correct stop line.
In the processing serving the aircraft; hooked up the wrong tow bar to the 737-9MAX.  Because; shortage of the tow bar.  The MAX tow bar from the gate was taken from other gate; it caused a confusion on the hook up.  When it was brought to the attention the tow bar was changed to the correct tow bar.
Ramp workers reported they used the wrong tow bar for a B737 MAX 9 aircraft and when they removed it the aircraft rolled because the brakes were not set.