Delta Air Lines Flight 723

Delta Air Lines Flight 723

Accident summary
Date	July 31, 1973
Type	Controlled flight into terrain
Site	Boston, Massachusetts, Logan International Airport (42°20′59″N 71°00′45″W / 42.349833°N 71.012519°W / 42.349833; -71.012519)
Passengers	83
Crew	6
Fatalities	89
Survivors	0
Aircraft type	McDonnell Douglas DC-9-31
Operator	Delta Air Lines
Tail number	N975NE

Delta Air Lines Flight 723 was a DC-9-31 twin-engine jetliner, registration N975NE, operating as a scheduled domestic passenger flight from Burlington, Vermont to Logan International Airport in Boston, Massachusetts, with an intermediate stop in Manchester, New Hampshire.^[1] On July 31, 1973 at 11:08AM, while on an ILS instrument approach into Logan in low clouds and fog, the aircraft descended below the glidepath, struck a seawall with a landing gear and crashed, killing all but two of its 89 occupants. Both survivors later died of their injuries.

Aircraft

The DC-9-31, registration N975NE, serial number 47075, was manufactured in September 1967 and had 14,639 flight hours at the time of the accident. The jetliner was one of the aircraft that Delta acquired in their 1972 merger with Northeast Airlines, to whom the aircraft was originally delivered.

Accident sequence

Delta Flight 723 final approach (plan view) from NTSB report; actual path flown (red) is shown in relation to nominal localizer path (blue); outer marker is shown as blue dot; flight direction is from left to right.

The aircraft, flying at 3,000 feet (910 m), had been vectored by Boston's approach control to intercept the final approach course to the ILS runway 4R approach at a 45 degree angle,^[2] about 2 nautical miles (3.7 km) outside the outer marker.^[3] As it was later revealed, the controller was busy handling a potential collision conflict between two other aircraft, and therefore neglected to clear Flight 723 for the approach. The flight crew had to ask the controller for approach clearance, which was immediately given, but by that time — more than a minute after the intercept vector had been issued — they were high and fast and almost over the outer marker. The flight crew subsequently failed to stabilize the aircraft's descent rate and airspeed, descended below the glideslope and drifted away from the localizer course, hitting a seawall about 165 feet (50 m) to the right of the extended runway centerline, about 3,000 feet (910 m) short of the runway's displaced threshold. The aircraft was destroyed, killing 87 of its 89 occupants. One of the two survivors died after two hours, and the other died of burn injuries on December 11, 1973.^[4]

The weather conditions at the time of the crash were partial obscuration and fog, with a ceiling of 400 feet (120 m), 1/2 mile visibility and light winds. Runway visual range (RVR) was 1,400 to 6,000 feet (1,800 m).^[3]

Investigation

Flight 723 descent profile, showing actual glide path flown (red), vs. nominal glideslope (blue), leading to crash point.

The NTSB investigated the accident and was able to retrieve both the CVR and FDR. The investigators concluded that, based on the retrieved flight data and simulations, the flight crew very likely operated the flight director improperly, inadvertently switching it into a "go around" mode during the final approach, instead of the appropriate approach mode. This caused confusion and additional pressure, and contributed to the unstablized approach and deviation from the glide path.^[1] According to the CVR, no altitude callouts were made by the crew during the final approach, as the aircraft descended below the glideslope and decision height, until it struck the seawall and crashed.^[3]

The board determined the following Probable Cause for the accident:^[3]

...the failure of the flightcrew 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 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.

Aftermath

Many positive changes were made in flight crew training and cockpit procedures after the accident in the years to come as a result of this accident in both internal company as well as industry-wide, and regulatory areas.

Delta has used Flight 723 as recently as October 13, 2011 for a Buffalo-Atlanta-Buffalo route.

Notes

	Boston portal
	Aviation portal

1. ^ ^{a b} "ASN accident record". ASN. http://aviation-safety.net/database/record.php?id=19730731-0. Retrieved 2009-07-14. 
2. ^ According to the NTSB report, 30 degree is the normal recommended maximum ILS intercept angle near the outer marker.
3. ^ ^{a b c d} "NTSB final report". U.S. Department of Transportation, NTSB. Archived from the original on 2008-02-28. http://web.archive.org/web/20080228064749/http://amelia.db.erau.edu/reports/ntsb/aar/AAR74-03.pdf. Retrieved 2009-07-14. 
4. ^ Struggle of Leopold Chouinard at CelebrateBoston.com