Date: 201909
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Light: Daylight
Aircraft: Q400
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Parked
Aircraft component: APU
Component problem: Improperly Operated
Reporter organization: Air Carrier
Reporter function: Captain
Reporter qualification: Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Human factors: Training / Qualification; Communication Breakdown; Situational Awareness
Anomaly: Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: Aircraft In Service At Gate; Pre-flight
Result: General None Reported / Taken
Contributing factors: Human Factors; Procedure
Primary problem: Procedure

Narrative: Flight crew left airplane to go on quick lunch break; PCA (Ground Power Cart) was hooked up batteries off. Temp in cabin was 61.When returned to the gate; the PCA was gone; APU started with the aircraft being heated. Cabin temp 81.Ramper informed me he took the PCA away and started APU to keep the aircraft cool. I asked him who authorized him to do that and he held his badge in front of my face with no communication. I said I didn't know what that meant he then pointed to the M on his badge; again with no communication from him. I again repeated my earlier statement. He then informed me he was part of the tow team and he could start the APU when he wanted and was advised by his supervisors to start the airplane to keep it cool. I asked to speak to his supervisors but he did not call them.A discussion ensued between us regarding his actions with us agreeing to disagree. Having tow team member start APU when they're not towing is a huge safety concern because there are no procedures outlined for flight crews to reconfigure flight deck if someone has changed flight deck except for Maintenance. A large percentage of rampers; gate agents and flight attendants are unaware of our SOP that states no passengers are authorized on board when the APU is running without the pilots being on board.The APU could fail without said tow team member realizing it since they are not sitting in flight deck and batteries could be drained. The ramper led me to believe this was a standard practice but after conducting a small poll the last few weeks I realized that no pilots are aware of this and no one informed pilots of this apparently standard practice by tow teams. This situation happened while it was still my airplane. Airplane was NOT getting ready to be towed. Upon further investigation and questioning by me with Maintenance personnel and other rampers; it appears that when rampers want to get warm or cool they run the APU at their discretion without regard to fuel costs. I believe this to be an unsafe practice for tow team members to start the APU when the airplane still belongs to the operating crew.I left the airplane in a certain configuration and come back to the airplane expecting it to be as I left it. When maintenance is performed on aircraft without us observing we have procedures outlined in our manuals to reconfigure flight deck. We have no such procedures outlined when another person comes on board and changes our configuration.It's a huge safety issue as the tow team; while taught how to turn on APU for electrical power while towing; has not been taught the heating/cooling systems of this airplane. Some Q400's can be quite a challenge to get the system dialed in. So when an individual who has not been taught such systems reconfigures that system then I have to reset the system and keep my fingers crossed that it'll work properly on the next flight. The tow team member; who was not towing the aircraft; had the heat on in an 80 plus degree day. Also while he said he was monitoring; he wasn't as temp cabin increased. What if APU fails and he doesn't realize it because he is either outside or inside cabin and doesn't hear it fail; and since he's not sitting in cabin he doesn't see the lights or hear the bell indicating APU failed. Now the batteries are being drained. My recommendation is that if aircraft belongs to a crew; the only person starting the APU should be Maintenance or the flight crew.




Synopsis: Q400 Captain reported unauthorized APU operations by ground personnel violated company policies and safety procedures.