CASM analysis in plain words: ask why unit cost moved and get a cited CASM-ex bridge, tied to the ledger and Form 41
Any unit-cost move explained in minutes, every cent tied to the ledger and Form 41.
See one case, screen by screen ↓CASM analysis explains an airline's cost per available seat mile — operating expense divided by available seat miles, in cents — and why it moved, usually as CASM-ex, which leaves out fuel. CASM Analysis brings airline unit cost analysis to FP&A: it answers any unit-cost question, for the system, a fleet or a station, with sources — eight AI agents build the bridge from the ledger, seat miles and Form 41, check it independently and draft the slide, and people approve and sign.
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CASM analysis is how an airline explains its cost per available seat mile, and investors grade a US carrier on CASM-ex — unit cost excluding fuel. When CASM-ex moves, the CFO has to say why on the earnings call and to the board. So after every close FP&A rebuilds the unit cost bridge by hand: a few hundred general ledger accounts mapped to cost categories, the CASM-ex exclusions taken out, seat miles from the schedule as flown checked against T-100, and the result reconciled to the Form 41 P-6 and P-12(a) schedules filed with DOT.
The reasons live below the accounts, so the cost analyst spends the week after close emailing payroll, tech ops and the integration office to ask why labor and maintenance moved. The bridge ends up in a spreadsheet only its author can follow, and every follow-up — excluding integration, by fleet, against peers — starts the rebuild again. Meanwhile the earnings number and the DOT filing can drift apart, and peers get compared without adjusting for stage length.
Estimated split of one quarterly CASM-ex bridge at a network carrier, in working days, by hand and with the solution. Review and sign-off stay with people.
Eight agents build each answer from the ledger, seat miles and Form 41 and check it; FP&A reviews, the CFO signs.
Corvane Airways, a network carrier with 304 aircraft and its hub at ORD, closed Q3 in the ledger on Monday, October 12. The earnings call is on the 22nd and the audit committee sees the board deck on the 27th. The CFO wants to know why CASM-ex rose. Here is the work in the working solution, screen by screen.
Laura's Today screen shows CASM-ex for Q3 2026 at 11.84¢, up 0.42¢ on Q3 2025, two questions waiting for an answer and one exception between the ledger and Form 41. When the ledger closed on Monday evening, the ledger agent mapped 214 accounts to 8 cost categories — $3,717.8M of CASM-ex cost on 31.40B seat miles — and overnight the check agent recomputed it independently: 0.00¢ from the answer.
Needs you: “Robert Castine asked: ‘Why did CASM-ex rise to 11.84¢ in Q3 from 11.42¢?’ · For the earnings call script (Thu, Oct 22) and the board deck · Due in 1 day.”
Laura clicks Answer it. The planner agent fixes the scope before anything runs: CASM-ex per definition v3, Q3 2026 against Q3 2025, the whole system. Then each step runs in view — the ledger agent reads the closed ledger, the capacity agent reads 31.40B seat miles against T-100, the driver agent reads the payroll register, shop-visit log and integration project ledger, and the Form 41 agent aligns it all to Schedule P-6.
“Scope: CASM-ex per definition v3, Q3 2026 against Q3 2025, whole system. Seven steps; I will show each one as it runs.”
“CASM-ex rose 0.42¢ to 11.84¢ in Q3 2026 from 11.42¢ a year earlier (+3.7%). Maintenance, labor and integration explain all of it; everything else nets to zero.” Maintenance adds +0.19¢ ($59.7M) from 11 engine shop visits on 787-9 engines against 4 a year ago; labor +0.15¢ from the 4.0% pilot pay step on July 1 and the flight attendant agreement; integration +0.08¢. A fleet strip underneath puts the 787-9 at 10.38¢, up 0.82¢.
Every driver shows how much of the move it explains and its confidence; the answer carries “Ties to the ledger · 0.00¢”.
Each driver carries its sources: GL 6310–6340, the Form 41 P-6 maintenance line and the shop-visit log for maintenance; GL 5100–5190, P-6 salaries and the pilot agreement §3.2 for labor. Opening one shows the passage itself — here the Q3 2026 Schedule P-6 draft, with maintenance material and repairs at 398.8 and the total at $4,927.0M, equal to the ledger.
Form 41 Schedule P-6 · Q3 2026 draft — “operating expenses by objective grouping · draft for filing · mapping table v12”.
The maintenance driver goes below the account to the events. The 787-9 page lists all 11 engine shop visits in Q3 — engine serial, ship, induction date, the work (high-pressure turbine blades, combustor, life-limited parts, performance restoration) and the cost, $53.9M in all. Three were pulled forward from Q4, which is why September is the highest month at 10.65¢.
The driver agent says “unexplained” rather than invent a reason; below a 90% explained floor it asks the owner.
Investor Relations needs one CASM-ex number excluding integration for the analyst Q&A file. Laura changes the question with one chip and the agents recompute: 11.76¢, up 0.34¢, with the $25.1M of Halden Air integration run-costs removed and maintenance and labor unchanged. Version 2 sits beside version 1, and Compare versions shows exactly what moved.
Check agent: “Both versions tie to the ledger at 0.00¢ and the draft P-6 equals the ledger at $4,927.0M. One thing to fix before filing: the T-100 seat count on six 787-9s is 0.14% below the seat miles flown.”
On Form 41 alignment Dana sees four exceptions. One needs her decision: July and August T-100 were filed at 290 seats on six reconfigured 787-9s that fly at 296, and the capacity agent has drafted the amendment for ships 3804, 3807, 3811, 3815, 3820 and 3823. The other three are explained — integration IT in P-6 “Other”, Halden Air July fuel booked in August, third-party maintenance excluded from CASM-ex — and she can accept them together.
“Agents prepare; Regulatory Reporting decides; Corvane files.”
From the answer, Laura saves to the board deck. The briefing agent drafts slide S-1 “CASM-ex Q3 2026: +0.42¢, three drivers”, slide S-2 for 11.76¢ excluding integration, and the earnings-script line. All three arrive In review, each tied to its answer version and sources. Laura approves them with reason A1, “Figures tied to the ledger and P-6”.
“Nothing enters the deck until the FP&A Director has reviewed it, Investor Relations has checked investor wording, and the CFO has signed.”
Simone approves the script line — “Third-quarter CASM-ex was 11.84 cents, up 3.7 percent year over year. Excluding integration run-costs, it was 11.76 cents, up 3.0 percent…” — with reason W1. Robert signs the unit-cost section with reason C1. Every item is locked to its answer version and sources, and a later change reopens review.
“Signed electronically … logged in the audit trail.”
The same CASM-ex move, seen by the five people who explain it, file it and sign it — what their quarter looked like, and what it looks like now.
Eight agents build each answer from the ledger, seat miles and Form 41 and check it; FP&A reviews, the CFO signs.
Reads the question and fixes the metric, definition, period, comparison and cut; asks when a question is ambiguous — year over year or sequential, CASM-ex or CASM with fuel.
Reads the closed general ledger, maps accounts to cost categories and removes the CASM-ex exclusions: fuel and fuel taxes, special items and third-party business expense.
Builds available seat miles from the schedule as flown and seat maps, by fleet and station, and checks them against the T-100 segment filings.
Explains each category's move from the payroll register, maintenance and engineering events, contract terms and the integration project ledger, with how much it can explain and its confidence.
Maps the ledger to Schedule P-6 objective lines, P-5.2 by aircraft type and P-12(a) fuel, and drafts fixes for differences.
Builds peer CASM-ex the same way for every carrier from public Form 41 P-6 and T-100 data, stage-length adjusted to 1,500 miles.
Recomputes every answer without seeing the first one and ties it to the ledger and the P-6.
Writes the narrated answer, the board slide and the earnings-script line with citations, and refreshes saved answers after each close, saying what changed.
Approve with a reason; sign the section; decide Form 41 fixes. The agents propose; a named person decides.
Ask on any screen, in plain words. Answers cite the ledger, Form 41 or T-100, and nothing changes until a person approves.
Why did CASM-ex rise to 11.84¢ in Q3?
Up 0.42¢ from 11.42¢: maintenance +0.19¢ (11 engine shop visits on the 787-9), labor +0.15¢ (July 1 pilot pay step), integration +0.08¢.
What is CASM-ex without integration?
11.76¢, up 0.34¢ (+3.0%): integration run-costs were $25.1M, 0.08¢.
Why is the A220-300 so much higher?
Short stages: 540 miles on average against 1,482 for the system, and integration run-costs land mostly on it — 17.27¢ without them. Stage length, not efficiency, explains most of the gap.
How do we compare in Q3?
Q3 Form 41 data for peers is not public until December. The latest like-for-like comparison is Q2 2026: 11.54¢ against 11.88¢. I will refresh this when Q3 posts and tell you what changed.
13 screens from the working solution, on its sample data. Pick one to see it large.
CASM-ex is defined once, signed by the CFO and used by every answer. Thresholds and rules are settings, and every change is logged.
| Setting | Default | Choose from |
|---|---|---|
| Tie-out tolerance to the ledger | 0.01¢ | Outside it, an answer cannot be board-ready |
| Flag a driver at | 0.05¢ | A category moving this much gets its own driver line |
| Explained floor | 90% | Below it, the driver agent asks the owner instead of guessing |
| Confidence floor | 80% | Below it, an answer says so in its first line |
| T-100 difference flag | 0.1% | Seat miles against T-100 |
| CASM-ex definition | v3, signed by the CFO Jan 15, 2026 | Excludes fuel and fuel taxes, special items and third-party business expense; propose a change, the CFO signs |
| Stage-length adjustment | To 1,500 miles | Used for peers only |
| Service levels | CFO question answered within 1 business day | Slide review within 2 business days · Form 41 exceptions closed 5 days before filing |
Every figure is labelled: a target the solution is built to, an estimate, a typical published result, or a proven one.
“demo” = seen in the working solution, on its sample Q3 2026 data · “target” = the design goal, measured in the live solution · “estimated” = our estimate (the stake per tenth of a cent is seat miles × $0.001; the days in “where a quarter's CASM bridge days go”) · “typical” = DWU Consulting on reading Form 41 (filings post a month or more after the period). Form 41 schedules (P-6, P-5.2, P-12(a)) and T-100 are named as context from BTS; definitions follow the MIT Airline Data Project glossary. People, Corvane Airways, Halden Air, peers, ship numbers, engine serials and amounts named on this page are fictional: characters and sample data in the working solution.
CASM analysis explains an airline's cost per available seat mile — operating expense divided by available seat miles, in cents — and why it moved, usually as CASM-ex, which leaves out fuel. CASM Analysis brings airline unit cost analysis to FP&A: it answers any unit-cost question, for the system, a fleet or a station, with sources — eight AI agents build the bridge from the ledger, seat miles and Form 41, check it independently and draft the slide, and people approve and sign.
CASM-ex is unit cost excluding fuel and other items the airline defines. In the working solution, definition v3 excludes fuel and fuel taxes, special items (merger advisory, severance, impairments) and third-party business expense, and keeps integration run-costs inside. The definition is versioned, signed by the CFO, and shown on every answer.
The ledger agent maps the closed ledger to cost categories, the capacity agent builds seat miles from the schedule as flown, and the driver agent finds the reasons in payroll, maintenance events and project ledgers. The bridge goes category by category from last year's CASM-ex to this year's, in cents or dollars, CASM-ex or CASM with fuel, with integration in or out.
Form 41 is the financial report large US airlines file with DOT under 14 CFR Part 241. The Form 41 agent maps the same ledger to its Schedule P-6 objective lines, P-5.2 and P-12(a) fuel, and the capacity agent checks seat miles against T-100. Differences become exceptions with a drafted fix; Regulatory Reporting approves or rejects each one with a reason.
The peer agent builds CASM-ex the same way for every carrier from public Form 41 P-6 and T-100 data and adjusts it to a 1,500-mile stage length. It says when peer data has not posted yet and never compares the CASM-ex in other airlines' earnings releases, because their exclusions differ. Peers stay anonymous on every slide.
No. The agents read closed periods only, never post or reclassify an entry, and never file with DOT. They draft fixes and slides; people decide.
Yes. Nothing enters the board deck until the FP&A Director has approved it, Investor Relations has approved the investor wording and the CFO has signed, each with a reason code. The check agent blocks board-ready outside the 0.01¢ tolerance, and every step is on a hash-chained audit trail.
The Agentic Solution Engine builds and deploys it from your requirements and documents — your CASM-ex definition, account mapping, seat-mile sources and Form 41 schedules — and it goes live once every quality gate has passed. We will walk you through it on your own closed quarter first.
Yesterday's flights earned by morning, and the revenue lost in suspense back on the books.
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