Incident Overview

Date: Tuesday 31 July 1973
Aircraft Type: McDonnell Douglas DC-9-31
Owner/operator: Delta Air Lines
Registration Number: N975NE
Location: Boston-Logan International Airport, MA (BOS) – ÿ United States of America
Phase of Flight: Approach
Status: Destroyed, written off
Casualties: Fatalities: 88 / Occupants: 89
Component Affected: Flight Crew (First Officer and Flight Director)Flight Crew (First Officer and Flight Director)
Investigating Agency: NTSBNTSB
Category: Accident
On Delta Flight 723, a descent caused by controller preoccupation resulted in a poorly positioned aircraft that exceeded its approach speed, striking a seawall. The flight director’s inadvertent use of go-around mode triggered instrument anomalies, leading to confusion and ultimately a catastrophic crash of a DC-9. The aircraft’s trajectory was significantly off course, resulting in a significant loss of life.On Delta Flight 723, a descent caused by controller preoccupation resulted in a poorly positioned aircraft that exceeded its approach speed, striking a seawall. The flight director’s inadvertent use of go-around mode triggered instrument anomalies, leading to confusion and ultimately a catastrophic crash of a DC-9. The aircraft’s trajectory was significantly off course, resulting in a significant loss of life.

Description

As Delta Flight 723 was descending, the approach clearance was given by the controller after a delay, because the controller was preoccupied with a potential conflict between two other aircraft. This caused the flight to be poorly positioned for approach. The aircraft passed the Outer Marker at a speed of 385 km/h (80 km/h too fast) and was 60 m above the glide slope. The flight director was inadvertently used in the ‘go-around-mode’, which led to abnormal instrument indications. This caused some confusion. The first officer, who was flying the approach became preoccupied with the problem. The DC-9 continued to descend and struck a seawall 3000 feet short of and 150 feet to the right of runway 04R, crashed and caught fire. RVR at the time was 500 m with 60 m overcast. All occupants, except one passenger, were killed in the crash. The lone survivor, who had been injured critically, died on December 11, 1973. PROBABLE CAUSE: “The failure of the flight crew to monitor altitude and to recognize passage of the aircraft through the approach decision height during an unstabilized precision approach conducted in rapidly changing meteorological conditions. The unstabilized nature of the approach was due initially to the aircraft’s passing the outer marker above the glide slope at an excessive airspeed and thereafter compounded by the flight crew’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.”

Primary Cause

Unstabilized precision approach conducted in rapidly changing meteorological conditions, exacerbated by the flight crew’s preoccupation with questionable information presented by the flight director system.Unstabilized precision approach conducted in rapidly changing meteorological conditions, exacerbated by the flight crew’s preoccupation with questionable information presented by the flight director system.

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