​​​Delta Air Lines Flight 723, a DC-9-31, crashed at 1108 eastern daylight time on July 31, 1973, while executing an instrument landing system approach to runway 4R on the Logan International Airport, in Boston, Massachusetts. There were 83 passengers, 5 crewmembers, and a cockpit observer on board. All occupants, except one passenger, were killed in the crash. The lone survivor, who had been injured critically, died later. The aircraft struck a seawall about 165 feet to the right of the extended runway centerline and about 3,000 feet short of the runway displaced threshold. The air craft was destroyed.

​We determined that the probable cause of ​passage of the aircraft through the approach decision height during an unstabilized the accident was the failure of the flightcrew to monitor altitude and to recognize precision approach conducted in rapidly changing meteorological conditions. The unouter marker above the glide slope at an excessive airspeed and thereafter compounded stabilized nature of the approach was due initially to the aircraft's passing the by the flightcrew's preoccupation with the questionable information presented by the flight director system. The poor positioning of the flight for the approach was in part the result of nonstandard air traffic control services.

​​As a result of this accident, we made recomendations to: ​

To the Federal Aviation Administration:

• ​Investigate the adequacy of the modification program, its implementation, and the quality control aspects monitored by the appropriate FAA Office. (A-73-062)
• Review the adequacy of the Delta Air Lines' quality control procedures in detecting and correcting the reported discrepancies. (A-73-063)
• Consider the necessity of imposing appropriate operational restrictions on the modified DC-9 aircraft until the underlying reasons for the avionics discrepancies have been identified and corrected. (A-73-064)
• Require that the Sperry Flight Director mode selection switch be modified to prevent inadvertent selection of the g/a mode. (A-74-1)
• Require an annunciator panel whenever any flight director system is installed. The panel would indicate electronically the mode in which the flight director is operating, regardless of the position of the mode selector switch. (A-74-2)
• Require that controllers receive formal training in procedures for using the approach light system monitor panel. (A-74-3)
• Revise air traffic control operational procedures to assure that the ground controller is provided, concurrently, with the same arrival sequence information that is provided the associated local controller. (A-74-4)
• Issue an Advisory Circular which describes the RVR equipment and emphasizes that the RVT valve is a sampling of a small segment of the atmosphere, usually near the touchdown point. It should also be emphasized that RVR value does not necessarily represent actual runway visibility conditions near the touchdown point and includes a significant time delay before reaching the crew. This information should also be placed in the airman's information manual. (A-74-19)