Narrative:

During a flight back to base after dropping a patient off I noticed that my transmission pressure indication was decreasing rapidly. I contacted dispatch and let them know that I would be diverting to [a nearby] airport and why. On final to the airport my transmission pressure indication came back to normal and throughout the situation I did not receive a cas message indication xsm pressure on my mfd. Upon landing I shutdown and contacted [operations] and informed them what was going on; and then proceeded to contact my maintainer on duty and inform him of the situation. [The mechanic] asked if I had written up the transmission pressure reading and at the time I had not. [He] then proceeded to tell me that all he was going to do was come out and have me do a ground run and see if the transmission pressure would drop again. He then said if I would conduct the ground run and then if no adverse condition arose to fly the aircraft back to base and he would take a look at it in the morning. I conducted the ground run and a hover check and all indications were in the green. En-route back to base my transmission pressure reading began to decrease and I made a [precautionary] landing in a parking lot. I then called the appropriate personnel and made an entry into the aircraft logbook stating a rapid decrease of transmission pressure was observed during cruise flight.I should have made an entry in the logbook at the first incident and not conducted maintenance over the phone.

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Original NASA ASRS Text

Title: BHT-407 helicopter pilot reported making a precautionary landing in a parking lot after the transmission pressure dropped.

Narrative: During a flight back to base after dropping a patient off I noticed that my transmission pressure indication was decreasing rapidly. I contacted Dispatch and let them know that I would be diverting to [a nearby] airport and why. On final to the airport my transmission pressure indication came back to normal and throughout the situation I did not receive a CAS message indication XSM pressure on my MFD. Upon landing I shutdown and contacted [Operations] and informed them what was going on; and then proceeded to contact my maintainer on duty and inform him of the situation. [The mechanic] asked if I had written up the transmission pressure reading and at the time I had not. [He] then proceeded to tell me that all he was going to do was come out and have me do a ground run and see if the transmission pressure would drop again. He then said if I would conduct the ground run and then if no adverse condition arose to fly the aircraft back to base and he would take a look at it in the morning. I conducted the ground run and a hover check and all indications were in the green. En-route back to base my transmission pressure reading began to decrease and I made a [precautionary] landing in a parking lot. I then called the appropriate personnel and made an entry into the aircraft logbook stating a rapid decrease of transmission pressure was observed during cruise flight.I should have made an entry in the logbook at the first incident and not conducted maintenance over the phone.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.