Date: 201809
Local time of day: 1201-1800
Location: ZZZ.Tower, US
Aircraft: P180 Avanti
Flight plan: IFR
Flight phase: Initial Climb
Airspace: Class D ZZZ
ATC / advisory: Tower ZZZ
Reporter organization: Government
Reporter function: Local
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Communication Breakdown; Situational Awareness
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter CFTT / CFIT
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert; Flight Crew FLC complied w / Automation / Advisory
Contributing factors: Procedure; Environment - Non Weather Related
Primary problem: Procedure

Narrative: I was working Local Control West (LCW); and Aircraft X called ready to go off Runway 1L. I cleared Aircraft X for takeoff at XA36; heading 300; which he read back. Approximately 2 miles north of the airport at XA38; Aircraft X tagged up on the radar; I told him to contact Departure and asked him to pass on flight conditions if able. He read back that he would like to return to Runway 1L. I issued him left closed traffic; cleared him to land on Runway 1L; and asked if he needed assistance; he said he did not and did not state the reason for return. At this time the Ground controller was coordinating with Approach; letting them know that Aircraft X was coming back to land. It appeared that Aircraft X had started a wide left turn into the downwind. About 4 miles northwest of the airport; at XA39; Aircraft X contacted me saying he had changed his mind and was requesting a frequency change. I was unsure of his intentions; since I was expecting him to join the downwind; and verified if he wanted to come back to land; to which he said no. At that point he was nearing the boundary of the Class D airspace; I switched him to departure for the second time; and he read it back. At this time the Ground controller coordinated with approach that Aircraft X was no longer returning to [the airport]; and that he's coming to them on a 300 heading. Approach acknowledged. Approximately 12 seconds later; at XA40; about 5 miles northwest of [the airport]; a Low Altitude alert went off for Aircraft X. Not sure if Aircraft X was still on my frequency; I issued the Low Altitude alert to him just in case. He was still on my frequency at that time; and read back that he will check his altitude. A short while later; Aircraft X flew in close proximity to obstructions northwest of [the airport]; The obstructions are 2300 MSL and Aircraft X was at 2600 MSL. Coordination with approach for a different heading when it is first noticed that the heading will take an aircraft directly toward the obstruction. If unable to coordinate a different heading; instruct the aircraft to climb without delay and keep him on my frequency; advise approach.


Second narrative: Aircraft X; departed Runway 1L at XA36. Two miles north of [the airport]; Aircraft X requested to return to Runway 1L. While the local controller was giving instructions for left traffic; I reminded them to ask if Aircraft X needed assistance. I coordinated with Approach that Aircraft X would be returning to [the airport]. Aircraft X did not require assistance. Aircraft X made a shallow left turn. While exiting the Class D airspace; Aircraft X decided to continue on their flight plan on a heading of 300. The local controller left Aircraft X on a 300 heading and switched the aircraft to Approach. (300 was assigned to Aircraft X initially as per our Letter of Agreement (LOA) with Approach). I coordinated with Approach. Seconds later the local controller was issuing a low altitude alert to Aircraft X. Aircraft X was still on [the airport] tower frequency. Aircraft X did not climb as expected. I don't know when Aircraft X finally contacted Approach; but they were definitely not at the altitude necessary for obstructions to the Northwest of [the airport]. Aircraft X's altitude indicated 026. There are towers at 023. I don't like that Aircraft X didn't want to tell us why they needed to return. I don't like that the pilot did not turn back into the downwind when instructed. I wound up in charge with an aircraft that didn't really need anything but was requesting to return to the airport while continuing out of my airspace. Once the pilot decided he wanted to continue; there were very few options left. The local controller was a recent check out. I discussed ways we could have provided better service in the moment. Such as holding onto the aircraft and coordinating a different heading. Or telling Aircraft X to expedite climb. (Although in reality the aircraft did not climb as expected).


Synopsis: Two Tower Controllers reported a P180 failed to change frequencies; which resulted in maintaining an altitude which triggered a low altitude alert.