Date: 201903
Local time of day: 1801-2400
Location: ZZZ.Tower, US
Aircraft: Small Transport
Flight plan: IFR
Flight phase: Final Approach
Airspace: Class B ZZZ
ATC / advisory: Tower ZZZ
Reporter organization: Government
Reporter function: Local
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Human-Machine Interface; Communication Breakdown; Situational Awareness
Anomaly: ATC Issue All Types; Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued New Clearance
Contributing factors: Human Factors; Procedure
Primary problem: Human Factors

Narrative: I was working Local position during a relatively slow period. Aircraft X came over to me on a visual approach on the inbound leg of the approach and the aircraft was west of course and descending slowly on the approach. The aircraft remained high on the approach and slightly west of course the entire time but appeared to be correcting. When the aircraft reached short final the ASDE (Airport Surface Detection Equipment) alerted with a taxiway alert. As required; I instructed the aircraft to go around at which point the pilot said unable we are single engine. I simply said roger and waited until the aircraft was safely on the ground to explain to the pilot why I had instructed him to go around.There are several issues with this scenario. First is the lack of communication. The lack of communication keeps valuable information from the people that need to know when something odd is going on; one of which was me; the Local Controller working the aircraft. The second issue is there was never an emergency called for the aircraft; my understanding is the aircraft did want to declare an emergency. We as air traffic controllers have the ability and should had declared for the aircraft. If an unplanned engine shutdown does not call for an emergency; I am not sure what would. In the event of an actual crash; the time it would had taken the airport fire department to reach the aircraft could had been used fighting fires and saving lives instead of traveling to the crash site. The third issue with this scenario is the ASDE alert for the taxiway. This feature is new and still has some issues; it does not allow for any approach other than a straight in. And most general aviation traffic on a VFR day on a VFR approach do not make perfect straight inbound legs. I could tell out the window that the aircraft was not aligned with the taxiway. The tolerance for the go around alert are too tight and needs to [be] addressed. When I instructed the aircraft to go around; luckily he said unable and continued in to land. I give this pilot credit for continuing; a lesser pilot who blindly follows ATC instruction may had performed a single engine go around which could had lead to a catastrophic event; resulting a torque roll which is a very real possibility in a light twin aircraft. So in my eyes there should had been an emergency called for the aircraft and the communication should had been better between the Tower Supervisor and the controllers; and the ASDE alert for the taxiways should be addressed.




Synopsis: Tower Controller reported an aircraft which they had not been notified had an engine out; refused their go around instruction for a false ASDE alert.