All you guys saying that manufacturer's procedures shouldn't be changed because they're thought out in accordance with the design philosophy... I only agree with you as far as they are actually thought out; and that is NOT necesarrily true!
For example I flew a King Air for two different jobs a while ago. In one of them (the first one) they had a company checklist that was organized for effecient operation (multiple legs a day and quick turns inbetween) as refined over decades of experience.
The other, well... they didn't use a checklist. But I did have access to a training center's sim checklist (marked "not for use in flight," which I did use in flight) and... the manufacturer's checklist!
Which was, in a word, atrocious. It had been designed by someone who thought of all the switch flips it takes to perform a flight and vomited them onto a few pages, with
zero thought put to how it might actually be used. Not even one practice run inside their head, let alone in a sim or even in front of a paper tiger or whatever.
For before engine start, there was no differentiation between an acceptance/origination/preflight/cockpit setup (whicever you want to call it) and the actual before engine start procedure. Everything was mashed up and interspersed in one. So, if you were to follow it strictly, you'd twiddle your thumbs and drink coffe while waiting for the passengers, and and after loading them up and their bags, you'd sit down in front of a clean slate and go through 5-10 minutes of setup and system checks, etc. whereas you could have done all of that
before, and now go just do 5 seconds of procedure and 10 seconds of checklist of the items only necessary to do immediately before the engine start.
Before takeoff - 12 items most of which could have been done earlier instead of clogging up time at the hold short line.
I was gonna give a blow by blow of all its problems for the whole flight, but hopefully you get the idea. But for the end, here I'll post the Landing checklist. Years later, I still can't get over how astoundingly stupid this is.
LANDING
Cabin sign.......................................................O N
Standby pumps...............................................ON
Flaps...............................................APPROACC H
Prop synch.....................................................OF F
Speed levers..................................................HIGH
Landing gear...............................DOWN, 3 GREEN
Flaps....................................................... ...100%
Landing and taxi lights...................................AS REQ'D
Pressurization............................................CH ECKED
Manual fuel/ignition......................................AS REQ'D
Power levers .................FLT IDLE, GND IDLE, REVERSE
Brakes....................................................AS REQ'D
Notice it starts with things you'd do at a few thousand feet, and ends with the rollout. There's no meaningful start and end point and no point at which you can perform it and say "approach checklist complete" or "landing checklist complete." "Power levers idle, Brakes as required..." gee ya think? Am I supposed to pull this out and read it right after I touch down to check those items? Or wait until a convenient time (stopped after landing) in which case if I forgot to pull the power to idle and apply brakes, I'll have already run off the runway and it's too late. It's not just difficult or onerous to use, but literally impossible.
After going through this experience, I can completely see the potential for lower-grade failures to think ahead to real-life operations even by modern airliner designers (such as the oxygen mask check being inconveniently at the end, from a few posts up). What it takes to do a test flight, which itself might be the center of maybe days or even weeks of organization, and the entire operation revolves around that flight, is not gonna be sufficient for the efficiency required to do routine 25 minute turns with flight attendants and gate agents and mechanics and dispatch in the picture.
In my only airline experience we have company-designed SOP's and checklists, and I'm actually very curious to see Bombardier's raw procedures for the CRJ.