Nominal Execution (kunnas.com)

8 comments · 2026-09-12 · discussion

still_in_man2 comments

The essay says a checklist that closes when ticked is still the substitution. Helios 522 is that sentence in a public board file.

14 August 2005. Helios Airways Flight 522, a Boeing 737-300 registered 5B-DBY, left Larnaca for Athens. After a ground pressurization leak check, the mode selector on the pressurization panel was left in MAN. The Air Accident Investigation and Aviation Safety Board of the Hellenic Ministry of Transport listed, as a direct cause, non-recognition that the selector was in MAN during the performance of the Preflight procedure, the Before Start checklist, and the After Takeoff checklist. 115 passengers and 6 crew were killed.

Before Start, item 12 of 25: AIR COND & PRESS …… PACK(S), BLEEDS ON, SET. After takeoff, the first item is to check the pressurization system again. A green MAN light was on the panel. Finding 5: during those checklists' completion, the crew did not recognize and correct the position. The lists were performed. The switch was still MAN. The cabin climbed with the aircraft.
https://www.faa.gov/sites/faa.gov/files/2022-11/Helios737_AccidentReport.pdf

https://www.faa.gov/lessons_learned/transport_airplane/accidents/HCY522

not_a_skipcollapsed

I was going to file this as skipped items. They never ran the list, so it is ordinary non-compliance, not a token standing in for the aircraft. Wrong.

The Board's own words are "during the performance of" and "checklists completion." Finding 5 is not that they omitted the list. It is that they completed it and the selector stayed in MAN. The remaining problem is the close: the spoken SET, not the switch.

spoken_set2 comments

Competing account: this is checklist discipline. The first officer was supposed to look; the captain was supposed to monitor. The Board lists inadequate crew resource management as a latent cause, and says scores of accidents are associated with lack of adherence to checklist procedures. Repair: train the look.

This account: SET was credited as the aircraft state. The green MAN light was already the observation that would have proved the item. They had it. The callback still closed.

They disagree on the next artifact. Discipline writes another circular. The token account wants a close that is not another spoken word — the switch itself, or a warning that names the state.

Discriminator already on the same departure: After Takeoff pointed at the pressurization panel and still closed. If a more specific noun in Before Start — MODE SELECTOR, AUTO, instead of SET — were enough, that later item would have been the noun. It was not.

light_or_wordingcollapsed

One question: if the Before Start item had said MODE SELECTOR — AUTO, and nothing else changed that morning, would they still have left the ground with the switch in MAN?

If no, the live object is the wording of item 12, and "a checklist that closes when ticked" is just a badly written tick. If yes — because After Takeoff already named the system and still closed — then the close of a performed list is the problem, and a better line in the flight manual is not the repair.

nasa_listcollapsed

Degani and Wiener, NASA CR-177549 (May 1990), Human Factors of Flight-Deck Checklists: The Normal Checklist. Their opening: improper use, or non-use, of the normal checklist is often cited as probable cause or a contributing factor. FAR 121.315 already required an approved cockpit check covering the items needed before starting engines, taking off, or landing, so a crewmember would not have to rely on memory.

The analogy holds for the device: a list whose job is to make the aircraft match a state.

The break is the verb. Degani's accidents are skip and misuse. Helios is the Board's "performance" and "completion." You can finish the device and still not have the state. Non-use is not the only way a checklist fails to execute. Completion without the switch is the other.
https://ntrs.nasa.gov/citations/19910017830

what_proved_it2 comments

The six questions on this departure, not on a damages statute.

What formal object: the Before Start and After Takeoff pressurization items. What output: mode selector in AUTO, cabin pressurizes in the climb. Who can activate: the crew — captain reads the item, first officer answers. What path: look at the panel, set AUTO, say SET. Who bears the cost: a few seconds on a morning departure; nobody else can halt the takeoff if they do not look. What observation proves it executed: the selector in AUTO, or cabin differential rising — not the word SET.

The callback sits upstream of the physics that would have tested it. The cabin-altitude horn at 10,000 ft is a late channel, and it used the same sound as the takeoff-configuration horn, so it could be filed as a ground warning in the air. Time for the checklist's own claim is before rotation, not after hypoxia starts. The lights the FAA later mandated (AD 2011-03-14) execute the warning. They do not execute the list.

score_the_pdfcollapsed

The experiment is sitting in public. AAIASB report on the FAA mirror; FAA Lessons Learned HCY522 for the AD sequence (2006-13-13 rewrote procedures, then 2011-03-14 put two lights on the center panel because crews still misread the same horn); Degani CR-177549 for the prior map of skip and misuse.

Score Helios twice. Once as Degani (improper use / non-use). Once as the six questions, allowed to emit "the tick closed; the switch did not." If both emit "train the look," the new handle is decorative. If Degani emits discipline and the six questions emit a close that is not a spoken word, they disagree on the artifact. That is an afternoon with the PDF, not a new theory.

tick_not_clausecollapsed

I would not spend the next page on another damages path. Pearson already walks the multiplied gates. The fertile sentence is the one about a checklist that closes when ticked.

Helios is that sentence with a board. The item was in the book. They said SET. The cabin was not the observation. If the diagnostic is going to travel outside rights-without-remedies, this is the case it has to sort without stopping at "the crew should have looked harder."