Aircraft Accidents and Lessons Unlearned LXXI: Delta Airlines Flight 723

At 11:08 Eastern Standard Time (EST), on July 31, 1973, Delta Airlines Flight 723 (DA723), a Douglas DC-9-31, registration number N975NE, struck the seawall during its approach to Runway 4-Right (4R) at Boston-Logan International Airport (BOS). The flight originated in Burlington Airport (BTV), Vermont, with a stop in Manchester Airport (MHT), New Hampshire, to pick up passengers stranded from a previous cancelled flight. The aircraft struck the seawall 165 feet to the right of the extended runway centerline, just beyond the SSW shoreline – controlled flight into terrain. The aircraft was 1-1/2 wingspans to the right of center. The accident number assigned was DCA74AZ004. There was no information available in the National Transportation Safety Board (NTSB) Archives.

The accident aircraft was airworthy; the flight crew was qualified. The NSTB accident report, AAR-74/03, “… determine[d] that the probable cause of the accident was 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 crew for the approach was in part the result of non-standard air traffic control services.”

N975NE in original Northeast Airlines colors

Not even close. For once, the cockpit voice recorder (CVR) actually held the answer. All the NTSB had to do was listen … really listen … to attitudes of those resisting a merger.

A May 15, 2021, article titled Mist on the Water: The Crash of Delta Flight 723 by Admiral Cloudberg, looked into the accident, albeit with dramatic overtones. Some information provided in the article was helpful in looking at the accident from a different perspective. However, aviationlessonsunlearned.com doesn’t refer to victims because, unless directly involved in the accident (like a hijacking or terrorist action) passengers have no bearing on the accident investigation results; they distract from the investigation. The victim approach is indicative of accident documentaries, where drama cancels facts.

The accident aircraft model, a DC-9-31, was designed as a two-man cockpit, where both pilots are/were interdependent in the performance of all their duties during the flight. Though dead-heading and restaging pilots frequently inhabit the cockpit to this day, they are/were not considered ‘flying’ crew members, meaning they didn’t actively participate in the flight’s piloting activities. In DA723’s case, a former Northeast Airlines captain – an Observer (OBS) – occupied the cockpit jumpseat; Northeast Airlines had merged with Delta the year before, in 1972. The AAR-74/03 report stated the OBS was, “… in the process of requalification after he was grounded for an extensive period of time because of illness.”

DA723 accident site looking down BOS runway 4-R

As a rule, the presence of a third person was normal. However, per The Crew Information page in report AAR-74/03, Appendix B, it was stated that the OBS was authorized to occupy the jumpseat, “… as an observer only [italics and bold added].” AAR-74/03, page 28, section 2.2 CONCLUSIONS (a) Findings #2 correctly stated, “The cockpit observer was not qualified to act as a flight crew member, nor was he authorized to participate in the conduct of the flight.” This random finding referred to the root cause. The OBS called out takeoff (10:51:32) and descent challenges (10:55:57). The OBS effectively disrupted normal communication flow between the captain and the first officer (FO).

This cannot be understated. The FO, as the flying pilot, and the captain, as the radio pilot on this leg, should’ve been working together – with only each other. Neither pilot should’ve been omitted from the normal cockpit conversations, especially below 10,000 feet. Climbing out of MHT, the FO asked if the challenge checklist was done, the captain said, “We’ll let Joe [the OBS] do it himself.” What? WHAT? This was a blatant disregard for procedure by the captain, who assigned the OBS to accomplish the challenge checklist by himself – to himself. Both flying pilots were deprived of critical information and cues for the safe approach. The OBS caused confusions throughout the short eighteen-minute flight.

The pilots violated the Sterile Cockpit Rule. Published January 19, 1981, Title 14 code of federal regulations (CFR) §121.542 (b) and Title 14 CFR §135.100 (b): “No flight crewmember may engage in, nor may any pilot in command permit, any activity during a critical phase of flight which could distract any flight crewmember from the performance of his or her duties or which could interfere in any way with the proper conduct of those duties, [underline added] such as eating meals, engaging in nonessential conversations within the cockpit … are not required for the safe operation of the aircraft.” Paragraph (c) of both subsections defines critical phases of flight, “… includes all ground operations involving taxi, takeoff and landing, and all other flight operations conducted below 10,000 feet, except cruise flight.”

The reader may note both regulations were adopted January 19, 1981, seven years after DA723. Also, neither regulation say the OBS couldn’t assist with pilot duties, such as checklist challenges. But the CVR transcript showed disruptions in crew duties were a problem (it was mentioned once in Finding #2). These cockpit conversations demonstrated the root cause of the accident: Confusion. The NTSB should’ve recommended to the Federal Aviation Administration (FAA) the CVR transcript presented irrefutable proof of the accident’s root cause and how to fix the problem. Instead, the NTSB missed the problem.

The fact that Title 14 CFRs §121.542 and §135.100 were adopted after DA723 doesn’t excuse responsibility for the confusion. Consider this: Checklist challenges were implemented long before Title 14 CFRs §121.542 and §135.100, long before the DA723 tragedy. Why? Title 14 CFRs §121.542 and §135.100 were written, among other reasons, to clarify the important role of the checklist challenges; not to introduce them, but to remove from doubt what the challenges’ purposes are. To assume DA723’s captain didn’t know the challenges’ purpose would not be true. Checklist challenges were created years before DA723 on purpose, intentionally; to be used each flight, specifically to avoid what did not happen in DA723, that important cues were missed between the captain and the FO, missed cues so critical they directly led, without question, to the accident.

As an FAA inspector, I flew many enroute inspections in airliner cockpits, sometimes with an airline check pilot next to me. Aside from watching for traffic out the window, neither the check pilots nor I … ever … assisted in pilot duties, just to prevent the confusions demonstrated in DA723. Anyone who’s flown in the cockpit during flight can testify that below 10,000 feet, such as takeoff, approach, landing, are the highest stress times of flight, that the captain-FO work relationship must never be interfered with.

The pilot disconnections could be ‘heard’ in the CVR transcript. 1 – The OBS corrupted the checklist’s purpose. 2 – The captain lost his authority during climb. 3 – The FO kept asking for information the captain should’ve provided automatically. One can even ‘hear’ (it is obvious to the trained ear) the FO’s reluctance to call out the OBS and captain for not providing him with critical information. Challenge questions should verify the pilot flying (in this case, the FO) is aware of the aircraft’s configuration, speed and altitude. Instead, critical information was lost and the CVR transcript left no ambiguity to these facts.

Cloudberg pointed out in his article that the flight director (FD) was incorrectly set to ‘Go-Around mode’, not ‘Approach’ mode as required for the landing. Per the article, “The problem was that the last mode on the [flight director] knob before the stop was go-around, not approach mode.” The article then referred to Northeast’s Collins FD-109 FDs being replaced by Delta’s Sperry Z-5-534 FDs for Delta’s DC-9 fleet. The article’s point was old FD setting habits were hard to break, even after Delta trained all three former Northeast pilots to correctly use the new FDs. Had the captain and FO conducted the checklist challenges – not the OBS – the ‘old FD setting habit’ would have been rectified because the captain and FO would have visually checked the ‘Approach’ setting. The OBS, who hadn’t flown since before the merger and FD transition, only knew the Collins FD; he introduced the confusion.

The captain allowed the OBS’s interference, encouraged it. The captain should’ve been monitoring the FO’s approach, kept his eyes on his own captain’s instrument panel to cross check the FO’s instruments. Both the captain’s and FO’s altimeters are to the right of the FDs, a mere flick of the eyes to check. This didn’t happen.

Another concern was the flight crew’s commitment to land under questionable circumstances. AAR-74/03 said the cockpit instrumentation was a problem: “… the flight crew’s preoccupation with the questionable information presented by the flight director system (FDS).” The FDS may have been a contributing factor, but it was unclear if it was a problem for the FO.

Absent from the CVR transcript was the FO, as flying pilot, didn’t confirm or deny he saw the field or the runway. BOS was obscured by fog that covered 3/10ths of the sky below 400 feet that gradually rose to 4/10ths by the time of impact. Eastern Airlines flight 1020’s captain, four minutes behind DA723 on its landing cycle, “… made a missed approach. The captain of flight 1020 stated that upon reaching the decision height (216 feet), he could see ‘nothing’ and initiated the missed approach.” The inability to find the runway – indeed the field, itself – should have been reason for the FO to go around.

Was the FDS out of alignment? Did DA723 have mechanical cause to approach 1-1/2 wingspans to the right of runway 4R’s centerline? The NTSB, as always, didn’t have any maintenance-qualified or avionics-qualified investigators to verify if instruments contributed to the accident. Instead, one NTSB board member prattled on about FD problems without any knowledge of the topic.

A question the NTSB also didn’t raise – a most obvious one – which was: Was there company pressure – from Delta Airlines – to bring DA723 into BOS for an on-time arrival? Sixteen years later Avianca Airlines flight 52 crashed because the airline pressured the flight crew to land in JFK during a weather event rather than divert to BOS before it ran out of fuel and crashed. Did something similar happen to DA723? We will never know because the NTSB didn’t pursue the question.

In the airline industry, pressure to meet a schedule can be significant; it’s understandable (not forgivable) how safety gets pushed aside for the good of the schedule. Like most NTSB investigations, obvious conflicts of interest, such as airline management pressures to meet schedules, were lost on investigators. Why didn’t NTSB operations investigators interview the Chief Pilot? Crew Scheduling? Flight Planning?

Fifty years ago, the NTSB faced a major accident they didn’t understand, namely the cultures that were at odds between Northeast Airlines and Delta Airlines. The merger and its resulting issues should have been front-and-center in this investigation because coincidences don’t exist. The NTSB has always been ignorant of how airlines work. Furthermore, the NTSB didn’t comprehend the fundamentals about mergers, that mergers are/were not just about merging assets, equipment, routes, and seniority lists. Merging cultures includes training to correct bad habits, unsafe habits.

The lack of professional cohesion between DA723’s flight crew was obvious to anyone, even those unfamiliar with cockpit procedures. The FO, as the pilot flying, needed assistance in dealing with BOS’s weather issues, cross referencing instruments, and concerns he had with the FD. The OBS entitled the captain by doing his job for him, then ignored the FO altogether. The captain? He had no authority in the cockpit, no control of the flight, from the moment they climbed out of MHT. He should’ve assured the FO maintained situational awareness and the OBS stayed quiet under 10,000 feet. The captain was also useless communicating with air traffic control.

Ignorance isn’t an excuse for missing important cues, for overlooking obvious conflicts in procedure and leading industry down a path to nowhere. DA723 was a lost opportunity for the NTSB to increase safety in the airline industry. After fifty years the NTSB still doesn’t understand the industry. ValuJet 592, US Air 405, National Air Cargo 102, Atlas 3591, among many examples the NTSB’s dismissal of root cause continues, and it comes from a lack of industry knowledge. NTSB aviation investigations have never been about accident prevention; they’ve been about being influential without the effort.