Delta Air Lines Flight 723
Encyclopedia
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
. 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.
, to whom the aircraft was originally delivered.
by Boston's approach control
to intercept the final approach
course to the ILS
runway 4R approach at a 45 degree angle, about 2 nautical miles (3.7 km) outside the outer marker. 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 (50.3 m) to the right of the extended runway centerline, about 3000 feet (914.4 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.
The weather conditions at the time of the crash were partial obscuration and fog, with a ceiling
of 400 feet (121.9 m), 1/2 mile visibility and light winds. Runway visual range
(RVR) was 1,400 to 6000 feet (1,828.8 m).
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. 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.
The board determined the following Probable Cause for the accident:
Delta has used Flight 723 as recently as October 13, 2011 for a Buffalo-Atlanta-Buffalo route.
Delta Air Lines
Delta Air Lines, Inc. is a major airline based in the United States and headquartered in Atlanta, Georgia. The airline operates an extensive domestic and international network serving all continents except Antarctica. Delta and its subsidiaries operate over 4,000 flights every day...
Flight 723 was a DC-9-31 twin-engine jetliner
Jetliner
Jetliner are an alternative rock band from the USA. They focus on melodic piano based rock and have been compared to Queen and early Elton John, being heavily influenced by early 70s rock. Composed of Adam Paskowitz of The Flys, son of Doc Paskowitz, on piano and lead vocals, Jeff Kluesner on...
, registration N975NE, operating as a scheduled domestic passenger flight from Burlington, Vermont
Burlington, Vermont
Burlington is the largest city in the U.S. state of Vermont and the shire town of Chittenden County. Burlington lies south of the U.S.-Canadian border and some south of Montreal....
to Logan International Airport
Logan International Airport
General Edward Lawrence Logan International Airport is located in the East Boston neighborhood of Boston, Massachusetts . It covers , has six runways, and employs an estimated 16,000 people. It is the 19th busiest airport in the United States.Boston serves as a focus city for JetBlue Airways...
in Boston, Massachusetts, with an intermediate stop in Manchester, New Hampshire
Manchester, New Hampshire
Manchester is the largest city in the U.S. state of New Hampshire, the tenth largest city in New England, and the largest city in northern New England, an area comprising the states of Maine, New Hampshire, and Vermont. It is in Hillsborough County along the banks of the Merrimack River, which...
. On July 31, 1973 at 11:08AM, while on an ILS
Instrument Landing System
An instrument landing system is a ground-based instrument approach system that provides precision guidance to an aircraft approaching and landing on a runway, using a combination of radio signals and, in many cases, high-intensity lighting arrays to enable a safe landing during instrument...
instrument approach
Instrument approach
For aircraft operating under instrument flight rules , an instrument approach or instrument approach procedure is a series of predetermined maneuvers for the orderly transfer of an aircraft under instrument flight conditions from the beginning of the initial approach to a landing, or to a point...
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 AirlinesNortheast Airlines
Northeast Airlines was an American airline based in Boston, Massachusetts. They began as Boston-Maine Airways, which was founded as a Pan Am contract carrier on July 20, 1931, by the Boston and Maine Railroad and Maine Central Railroad offering service from Boston to Bangor via Portland...
, to whom the aircraft was originally delivered.
Accident sequence
The aircraft, flying at 3000 feet (914.4 m), had been vectoredAircraft vectoring
Aircraft vectoring is the term given to a navigation service provided to aircraft by air traffic control. The controller decides on a particular pattern for the aircraft to fly, composed of specific legs or vectors...
by Boston's approach control
Terminal Control Center
A terminal radar approach control is an air traffic control facility usually located within the vicinity of a large airport. Typically, the TRACON controls aircraft within a 20-50 nautical mile radius of the major airport and a number of "satellite airports" between surface and up to between and...
to intercept the final approach
Final approach (aviation)
A final approach is the last leg in an aircraft's approach to landing. In aviation radio terminology, it is often shortened to "final".In a standard airport landing pattern, which is usually used under visual meteorological conditions , aircraft turn from base leg to final within one to two miles...
course to the ILS
Instrument Landing System
An instrument landing system is a ground-based instrument approach system that provides precision guidance to an aircraft approaching and landing on a runway, using a combination of radio signals and, in many cases, high-intensity lighting arrays to enable a safe landing during instrument...
runway 4R approach at a 45 degree angle, about 2 nautical miles (3.7 km) outside the outer marker. 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
Airspeed
Airspeed is the speed of an aircraft relative to the air. Among the common conventions for qualifying airspeed are: indicated airspeed , calibrated airspeed , true airspeed , equivalent airspeed and density airspeed....
, descended below the glideslope and drifted away from the localizer course, hitting a seawall
Seawall
A seawall is a form of coastal defence constructed where the sea, and associated coastal processes, impact directly upon the landforms of the coast. The purpose of a seawall is to protect areas of human habitation, conservation and leisure activities from the action of tides and waves...
about 165 feet (50.3 m) to the right of the extended runway centerline, about 3000 feet (914.4 m) short of the runway's displaced threshold
Displaced threshold
A displaced threshold is a runway threshold located at a point other than the physical beginning or end of the runway. The portion of the runway so displaced may be used for takeoff but not for landing...
. 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.
The weather conditions at the time of the crash were partial obscuration and fog, with a ceiling
Ceiling (cloud)
- ICAO :The height above the ground or water of the base of the lowest layer of cloud below 6000 meters covering more than halfthe sky.- United Kingdom :...
of 400 feet (121.9 m), 1/2 mile visibility and light winds. Runway visual range
Runway visual range
Runway Visual Range is a term used in aviation meteorology to define the distance over which a pilot of an aircraft on the centreline of the runway can see the runway surface markings delineating the runway or identifying its centre line...
(RVR) was 1,400 to 6000 feet (1,828.8 m).
Investigation
The NTSB investigated the accident and was able to retrieve both the CVRCockpit voice recorder
A cockpit voice recorder , often referred to as a "black box", is a flight recorder used to record the audio environment in the flight deck of an aircraft for the purpose of investigation of accidents and incidents...
and FDR
Flight data recorder
A flight data recorder is an electronic device employed to record any instructions sent to any electronic systems on an aircraft. It is a device used to record specific aircraft performance parameters...
. The investigators concluded that, based on the retrieved flight data and simulations, the flight crew very likely operated the flight director
Flight director (aviation)
In aviation, a flight director is a navigational aid that is overlaid on the attitude indicator that shows the pilot of an aircraft the attitude required to follow a certain trajectory.-Description:...
improperly, inadvertently switching it into a "go around
Go-around
A go-around is an aborted landing of an aircraft that is on final approach.- Origin of the term :The term arises from the traditional use of traffic patterns at airfields. A landing aircraft will first join the circuit pattern and prepare for landing in an orderly fashion...
" 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. 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.
The board determined the following Probable Cause for the accident:
...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.