Date: 201606
Local time of day: 0001-0600
Location: A90.TRACON, NH
Light: Night
Aircraft: A319
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Flight phase: Final Approach
Airspace: Class B BOS
ATC / advisory: TRACON A90
Reporter organization: Government
Reporter function: Approach
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Troubleshooting; Situational Awareness
Anomaly: ATC Issue All Types; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter CFTT / CFIT; Inflight Event / Encounter Unstabilized Approach
Detector: Person Air Traffic Control; Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Flight Crew Executed Go Around / Missed Approach; Flight Crew Requested ATC Assistance / Clarification
Contributing factors: Airspace Structure; Procedure
Primary problem: Procedure

Narrative: Aircraft X was being vectored for the Light Visual Approach to runway 33L at BOS. The aircraft was level at the assigned altitude of 1800 feet (the crossing altitude on the approach). I issued a clearance direct LYHTT. Soon after I observed the aircraft at 1700 feet which drew my attention but didn't draw any alarm as mode C often varies 100 feet. When I observed the very next hit at 1500 feet I issued a low altitude alert and the crossing altitude at LYHTT.As I was speaking the next hit came at 1300 feet and you can hear the MSAW alert in the background. The pilot simply responded with a hurried 'roger'. The aircraft continued a descent to 1000 feet when I issued instructions to again check altitude immediately followed by a heading and altitude to maintain. Again; a hurried 'Roger'. The descent from level flight at 1800 feet to 1300 feet occurred in less than 10 seconds. That's a 3000 foot per minute descent rate from level flight. In the end; I vectored the aircraft out to a 10 mile straight in and the aircraft landed without incident.The Light Visual Approach was developed for midnight operations to accommodate noise abatement. Since its inception; there has been a common feeling that this approach was potentially unsafe due to its extreme complexity requiring large turns at low altitudes; at night; over the ocean when pilots are most fatigued. One of the turns is about 60 degrees at 1000 feet to a 3.5 mile final. Most airlines require the aircraft be on glide path; at approach speed; in landing configuration; and with wings level by 1000 feet.It is my opinion that this approach works in contradiction to today's safety standards with regards to aircraft performance; airline requirements; and fatigue concerns. While one may argue that this approach has been successfully flown without issue by countless aircraft; it is fact that there have been issues in the past (missed approaches; etc) due to flyability of the approach. With today's fleet of aircraft and the overwhelming desire to stress the importance of stable approaches; it is my opinion that this approach is no longer a valid option due to safety concerns.




Synopsis: A90 TRACON Controller reported an aircraft conducting a published charted visual approach descended below the minimums and executed a missed approach.