Daniel and Hannah flew back to Israel recently on a Portuguese ACMI operator called High Fly. He says it was a 767 wearing someone else's livery, crew speaking Portuguese over the PA, and the passengers around him clearly thought they were on an Israeli airline. That got him reading up on how wet leasing actually works, and the part that snagged his attention was this: the crew flies under High Fly's operating license, not the chartering airline's. So the pilots are flying to High Fly's standard operating procedures, not El Al's or whoever sold the ticket. And his questions are... how different are those SOPs between operators, really? Are we talking dozens of variants or just a few tribes? Can a passenger ever notice the difference? And how do pilots who bounce between operators keep their brains from locking into one company's way of doing things?
To answer that, we need to start with what an SOP actually is, and what it isn't.
Go on, then.
An SOP is the airline's written bible for how every phase of flight gets conducted. It's not just the checklist you see them flipping through. It's the callouts, the flows, the automation logic, the hand-flying philosophy, even how you physically reach for a switch. Left hand or right hand. Thumb or index finger. Some operators specify this down to the grip.
I've seen pilots on the 737 stab at the overhead panel with a finger while the other hand stays on the yoke. That's... written down somewhere?
It is. And the critical thing, the part most coverage gets wrong, is where SOPs sit in the regulatory stack. At the bottom you've got the aircraft flight manual, the AFM, which is the manufacturer's document approved by the regulator. That's the floor. Then above that you've got the type rating, which certifies a pilot to operate that aircraft category. But the SOPs sit above both of those. The airline writes them, and they can be more restrictive than the AFM, but never less restrictive.
So the type rating says "here's how you fly a 767." The SOP says "here's how WE fly a 767."
And both the FAA and EASA formally recognize what they call acceptable variants. The idea is that multiple procedural solutions can achieve equivalent safety outcomes, and operators are free to choose among them as long as they document and train to their chosen variant. So when High Fly operates a flight for El Al, the crew follows High Fly's SOPs, not El Al's. Even though the passengers are sitting in an El Al seat, eating an El Al meal, looking at an El Al safety card. The procedures in the flight deck are Portuguese.
Which is the whole premise Daniel's poking at. So with that framework in place, let's look at where the variation actually lives.
The first thing to understand is that we're not talking about hundreds of individual operator silos. The industry has roughly settled into three or four major tribes of SOP philosophy. There's the Airbus tribe, which is heavily standardized across most Airbus operators because Airbus baked the procedures into the aircraft's logic from the start. The callouts, the automation management, the flight mode annunciator responses... they're remarkably consistent from one A320 operator to the next.
And the Boeing side?
More fragmented. You've got what I'd call the Boeing traditionalist tribe, which tends toward more captain discretion and less rigid automation management. Then the low-cost carrier tribe, which runs highly abbreviated flows because they're optimizing for twenty-five-minute turns. Single-pilot cockpit tasks during cruise, minimal callouts, everything stripped to the bone. And then the legacy flag-carrier tribe, which is more verbose, more callouts, stronger hierarchy gradient between captain and first officer.
That hierarchy piece is interesting. You're saying the same aircraft type flown by an LCC crew versus a flag-carrier crew will sound different in the flight deck?
Completely different. Let me give you a concrete example. The approach brief. This is the structured briefing the pilots give each other before they start descending toward the airport. At one airline, the pilot flying briefs the entire approach from the initial approach fix all the way through the missed approach procedure. Every waypoint, every altitude, every radio frequency. At another airline, the pilot monitoring briefs the missed approach while the pilot flying briefs the approach itself, so it's a split brief. At a third, the brief is a scripted read-back of the approach plate with zero deviation permitted. You read what's printed, in the order it's printed, and you don't add commentary.
All legal.
All legal, all produce the same outcome, and all fall within the acceptable variant framework. But a pilot switching between them has to unlearn their muscle memory for who speaks when. If you've spent five years at an airline where the PM handles the missed approach brief, and then you move to one where the PF does the whole thing, you will find yourself opening your mouth at the wrong moment. And that hesitation, that half-second of cognitive friction, is exactly where errors start.
So the difference isn't in what gets done. It's in who does it, when, and in what order.
And how. Let's talk about automation management philosophy, because this is where the variation gets significant. Some operators mandate autothrust and flight directors on until five hundred feet above ground level. Hands off, let the aircraft fly the profile, monitor only. Other operators require hand-flying from two thousand feet. Some forbid using the autopilot below one thousand feet in visual conditions. Others leave it entirely to captain's discretion.
That's not a trivial difference at five hundred feet.
It's not. It changes the cognitive load distribution in the critical final phase of flight. If you're hand-flying from two thousand feet, you're managing pitch, power, and configuration manually while also monitoring the approach path and looking for the runway environment. If you're on autothrust until five hundred, you're in a monitoring posture for much longer, and then you have a compressed window to transition to manual control. Both approaches have safety rationales. The hand-flying-early school says you build situational awareness by being physically engaged. The automation-late school says you reduce workload during the busiest phase so you can focus on decision-making.
And a pilot who's done it one way for a decade suddenly has to do it the other way because they changed operators.
Or because they're flying for an ACMI carrier this week. Here's a third example, and this one is almost comically small but it matters. The thousand-foot callout. On final approach, when the radar altimeter reads one thousand feet above the ground, one of the pilots makes a callout. At some airlines, the callout is "one thousand." At others, it's "thousand." At others, it's "one thousand above." Some require the pilot monitoring to add "stable" or "unstable" after it.
Wait. If you say "thousand" at an airline that expects "one thousand," that's a procedural deviation?
It is. The meaning is identical. Everyone in the flight deck knows exactly what altitude is being called. But the SOP is the SOP, and if the cockpit voice recorder gets pulled and the callout doesn't match the operator's written procedure, it's a finding. That's the level of granularity we're talking about.
That's... so the word "one" is the difference between a clean flight and a paperwork item.
And when you're operating under an ACMI certificate, the regulator holding that certificate can audit those callouts. The Portuguese authority, in High Fly's case, expects to hear High Fly's callouts, not El Al's.
So we've got tribes, not hundreds of individual variants. But within those tribes, the differences are real and they go right down to individual words.
And it gets messier. There's a phenomenon called procedural drift. Even within the same airline, SOPs evolve through safety bulletins, fleet-specific memos, and informal captain preferences. A senior captain who's been flying the line for twenty years might have a slightly different way of running a flow than what's written in the latest revision of the manual. New first officers learn the manual version in the sim, then get on the line and discover the captain does it differently. That creates de facto sub-variants that complicate cross-fleet flying.
So even if two airlines have nominally the same SOP tribe, the lived reality in the flight deck might have drifted apart.
And ACMI crews deal with this constantly. They're moving between operators, between fleets, sometimes between aircraft types, and they have to know which version of which procedure applies today.
Those are the mechanics of variation. But the question Daniel really wanted answered is whether any of this matters to anyone outside the flight deck.
The short answer is yes, but only in specific, rare circumstances. A passenger might notice a different flap setting on approach. On the seven thirty-seven, for example, some operators use flaps three for a given approach while others use flaps five. Flaps three is a lower drag configuation, which means a slightly higher approach speed and a slightly flatter pitch attitude. Flaps five gives you more drag, steeper descent, slower speed. A passenger who flies the same route regularly and pays attention might notice that the aircraft feels different on final.
Feels different how?
With flaps three, the nose is lower, the engines are spooled a bit higher, and the touchdown can be firmer because you're carrying more speed. With flaps five, the nose is higher, the descent feels steeper, and the landing tends to be softer because you're slower. Neither is wrong. Both are operator SOP choices.
What else might a passenger notice?
The descent profile. Some operators use a continuous descent approach where the aircraft basically idles down from cruise to the final approach fix with minimal level-offs. Other operators use a stepped-down approach with multiple level segments. The continuous descent is quieter and more fuel-efficient. The stepped approach gives the crew more time to configure and brief. A passenger might notice that on one airline the engines seem to spool up and down several times during descent, while on another it's a smooth, quiet glide all the way down.
I've definitely noticed that difference and never knew what I was hearing.
The one thing a passenger is most likely to notice, though, is the cabin crew's pre-landing announcement timing. Some operators require the cabin secure call at ten thousand feet. Others at five thousand. Others trigger it when the seatbelt sign is switched on by the flight deck, which could be anywhere from fifteen thousand feet down to eight thousand depending on weather and traffic. This timing is driven by the flight crew's SOP for when to arm the seatbelt sign, which varies by operator.
So you're sitting there, the seatbelt sign dings on, the cabin crew scrambles to secure the galley, and whether that happens at ten thousand feet or five thousand feet is actually a written procedure in a manual somewhere.
And if you fly the same route on different airlines, you'll notice the rhythm is different. On one airline, you get the announcement, then fifteen minutes of cruising at low altitude before landing. On another, the announcement comes and you're on the ground four minutes later.
But ninety-nine percent of SOP variation is invisible from the cabin.
Completely. The callouts, the flows, the automation logic, the hand-flying philosophy... none of that reaches the passenger. Which brings us to the other question Daniel asked, and this is the one that really matters for safety. How do pilots maintain a type rating across multiple operators without baking in one operator's SOPs?
Because if you've flown a seven sixty-seven for High Fly for two years, and then you pick up a contract with another ACMI operator, you're still type-rated on the seven sixty-seven. But the SOPs are different.
And the answer is, it's difficult, and it requires deliberate cognitive separation. Experienced pilots who fly for multiple operators develop what's called procedural compartmentalization. They build a mental mode switch where they consciously activate the SOP set for whichever operator they're flying for that day. This isn't something you just pick up. It's trained through operator-specific line-oriented flight training, what the industry calls LOFT, and through recurrent simulator sessions that explicitly practice the transitions.
So before you fly your first line flight for a new operator, you go into a sim and you fly their procedures?
You do, and you also go through a formal differences training course. When a pilot moves between operators on the same type, they undergo a differences module that explicitly highlights the SOP deltas. These courses can be as short as two days or as long as two weeks, depending on how far apart the operators' SOPs are.
Two days seems... short.
It can be, if the operators are in the same tribe. If you're moving from one Airbus operator to another, the differences might be minor. A few callout changes, a slightly different flow for the before-start checklist. Two days of ground school and a sim session might cover it. But if you're moving from a Boeing traditionalist operator to a low-cost carrier, or from a flag carrier to an ACMI operator, the gap can be substantial. Two weeks of training, multiple sim sessions, and a line check at the end.
And the risk if you don't get this right?
Negative transfer. That's the term of art. It's when a pilot instinctevely performs a procedure from operator A while flying for operator B, especially under stress or fatigue. The classic case study here is Flydubai flight nine eighty-one, the twenty sixteen accident in Rostov-on-Don. The final report from the Russian Interstate Aviation Committee and the GCAA identified SOP confusion as a contributing factor. The crew had previous experience on the seven thirty-seven with different operators, and during the go-around, they performed actions that were consistent with their prior operator's procedures but not with Flydubai's. The aircraft entered an upset and impacted the ground.
That's... that's the worst-case scenario made real.
It's exactly what the differences training is designed to prevent. And it's why regulators have tightened the requirements. EASA and the FAA now require ACMI operators to provide SOP familiarization materials to leasing crews. Some wet-lease contracts go further and specify that the lessor's crew must undergo the lessee's SOP training if the gap is wide enough.
Which effectively blurs the ACMI SOP boundary.
It does. The whole point of ACMI is that the lessor provides the crew, the maintenance, and the insurance, and the lessee just buys capacity. But if the lessee's SOPs are so different that the lessor's crew needs to be trained in them anyway, you've partially defeated the purpose of the arrangement.
Or you've created a hybrid model where the crew flies the lessor's procedures for most phases but adopts the lessee's callouts and flows for the phases that interface with the lessee's operation.
Which is actually happening. I've seen contracts where the ACMI crew flies their own SOPs for flight deck operations but adopts the chartering airline's procedures for anything that touches cabin crew coordination, because the cabin crew are from the chartering airline and they're trained to a different rhythm.
So the flight deck is speaking Portuguese, metaphorically, but the cabin interface is in Hebrew.
That's a cognitive split that adds workload. The pilots are managing two procedural frameworks simultaneously. Most handle it fine. Most of the time. But when something goes wrong, that's when the seams show.
Hilbert: I own one.
...What?
Hilbert: Well, several. The manuals, I mean. I've got the differences training binders from three operators on my shelf. Airways Leasing, early two thousands. I was a ground instructor there for about eighteen months.
You wrote the differences manuals.
Hilbert: For the seven fifty-seven and seven sixty-seven fleets. The thing nobody talks about is that the SOP differences aren't just in the flight deck. They're in the paperwork. I spent six months reconciling the fuel reporting forms. One operator wanted fuel in kilograms, another in pounds, another in US gallons, and one wanted it in hours of fuel remaining calculated by the captain.
The same aircraft, the same fuel load, four different ways of writing it down.
Hilbert: If the form was wrong, the finance department wouldn't pay the fuel bill. That's the kind of SOP difference that never makes it into the training manual but will get a pilot in trouble on day one. You land in Lagos, you've been awake for fourteen hours, you're filling out a fuel receipt in pounds when the operator wants kilograms, and three weeks later someone in accounts is asking why there's a discrepancy on the invoice.
Did you have to train pilots on that?
Hilbert: I put together a forty-page appendix. Just fuel forms. The pilots hated it. They'd sit through four hours of differences training on callouts and flows, and then I'd hand out the fuel form appendix and you could see the life drain out of them.
That's the part of the job nobody thinks about when they sign up for ACMI flying.
Hilbert: There was one operator, I won't name them, that required the captain to initial every fuel uplift slip personally. Another operator allowed the first officer to sign. Seems trivial. But we had a two-week delay certificating a crew for a wet-lease contract because the lessee's auditors insisted on the captain-only rule and our crews had been trained the other way.
Two weeks over whose signature goes on a fuel slip.
Hilbert: The auditors argued it was a command authority issue. If the first officer signs, the captain hasn't verified the uplift personally. Our position was that the first officer is a qualified crew member and the captain reviews the slip regardless. They wouldn't budge. Two weeks of back-and-forth while the aircraft sat on the ground.
That's the kind of detail that never makes the safety report.
Hilbert: I've still got the correspondence. It's in a box somewhere.
The fuel form thing actually connects to something we didn't touch on. The administrative SOPs, the ones that live outside the flight deck, they're often the ones that cause the most friction in ACMI arrangements because nobody thinks to harmonize them. Everyone focuses on the flying procedures. But the finance department's requirements, the maintenance logging conventions, the way defect reports are written... those are SOPs too, and they're just as operator-specific as the thousand-foot callout.
Hilbert: We had one lessee that wanted all maintenance snags written in English. Our maintenance provider wrote them in Portuguese. That took three months to sort out, and it had nothing to do with how the aircraft was flown.
The ACMI model works, but the seams are everywhere once you look past the flight deck door.
Hilbert: It works because the crews are professionals and they figure it out. But the system doesn't make it easy for them.
That's the kind of detail that never makes the safety report. So where does this leave us?
With an open question, I think. The ACMI market grew twelve percent in twenty twenty-five. That's a lot of wet-leased capacity, a lot of crews moving between operators, a lot of differences training courses being written and delivered. And the question is whether we'll see pressure toward SOP standardization across operators to reduce the negative transfer risk.
Or whether the diversity of SOPs is actually a feature, not a bug.
There's an argument for that. The acceptable variants framework exists because no one has definitively proven that one way is safer than another. Having multiple approaches means the industry can evolve. If everyone standardizes on one set of callouts and one automation philosophy, you lose the variation that lets you discover better ways of doing things.
But the cost is what we've been describing. Pilots carrying the cognitive load of switching between frameworks, and occasionally, in the worst cases, getting it wrong.
That tension is about to get sharper. The industry is moving toward reduced-crew cockpits and eventually single-pilot operations. If the remaining pilot has to switch between operator SOPs without a second pilot to cross-check, the margin for procedural error shrinks dramatically. You can't afford a negative transfer event when there's nobody sitting next to you to catch it.
The ACMI SOP question, which feels like a niche operational detail right now, becomes a central safety issue in a reduced-crew world.
It does. And I don't think the regulators have fully grappled with that yet. The differences training framework was built for a two-pilot world where the other pilot is the backstop.
The next time I board a plane with a crew that doesn't match the airline's nationality, I'll remember this. The procedures they're following might be completely different from what the airline's own pilots use. And that's by design, not by accident.
That's the thing Daniel spotted from his seat. The livery says one thing. The operating certificate says another. And the SOPs in the flight deck belong to the certificate, not the paint job.
We should thank Hilbert Flumingtop for producing, and for the fuel form appendix none of us knew we needed.
This has been My Weird Prompts, the human-AI collaboration podcast. If you want to send us your own questions, email the show at show at my weird prompts dot com.
We'll be back soon.
