Date: 202007
Local time of day: 0601-1200
Location: N90.TRACON, NY
Flight conditions: VMC
Light: Daylight
Aircraft: Hawker 900
Operator: Air Carrier
Operating under: Part 135
Flight plan: IFR
Mission: Passenger
Flight phase: Climb
Airspace: Class C ZZZ
Aircraft component: Fire/Overheat Warning
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Human factors: Confusion
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Weight And Balance
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew FLC Overrode Automation; Flight Crew Diverted; General Maintenance Action
Contributing factors: Procedure; Aircraft; Human Factors
Primary problem: Aircraft

Narrative: Captain and I were flying Aircraft X on a 135 leg between ZZZ and ZZZ1. Prior to this leg; we had repositioned the aircraft from ZZZ2 without incident. Due to the leg length; we fueled with 9;000 lbs. of fuel prior to departure. During climbout; at approximately 7;000 ft. MSL; the Master Warning System flashers activated; followed shortly thereafter by a REAR BAY OVERHEAT indication. The indication went away after a few (less than 10) seconds; followed by a reactivation of the MWS with no REAR BAY OVERHEAT indication. I was the pilot flying while Captain was Pilot Monitoring. I continued to fly while he handled the other duties. I believed the best course of action was to get the aircraft on the ground as soon as practicable; my training and systems knowledge (the bay overheat sensor is part of the Fire Detection and Suppression system) led me to believe that this is an emergency detection system without a suppression component; I.e there is no way to mitigate the effects of the overheat condition other than closing the air bleed valves. I knew that we would be faced with an overweight landing condition since we had just departed with a takeoff weight approximately 3;000 lbs. above maximum landing weight. For that reason; I advocated landing at an airport with a long runway; the closest of which was ZZZ3. Since the indication had gone away we did not request priority handling with ATC. Approach and landing were made without incident; and in accordance with the overweight landing checklist. I explained the situation to the passengers once we landed and conducted an exterior walkaround of the aircraft; with no abnormalities noted. Landing weight was approximately 26;000 lbs.At the time of the incident; I was under the impression that the memory items for this indication had been completed; however since then I have learned that there was a delay in the event and completing the memory items. Obviously; I should have been aware of this at time of the incident and represents less than optimal communication between ourselves. I do not however; believe this would have impacted the ultimate decision; which was to terminate the flight based on an emergency indication. To have continued the flight; or to have delayed landing after such an indication in the interest of continuity of an operation; would have been unwise.




Synopsis: Captain reported a Rear Bay Overheat Warning; causing a diversion.