Originally Posted by
galdian
If I have a suspected Airspeed Unreliable why would you do anything except maintain standard takeoff pitch - 15 degrees - and maybe tweak power back to MCT, sit fat dumb and happy until MSA THEN start screwing around with things?
You can do anything you want - as long as you can justify it.
To me achieving MSA then doing the Airspeed Unreliable checklist increases the safety of the aircraft, that's what I'd explain to those lined up against me at the enquiry - just remember the warm and fuzzy feelings Sully and the F/O received! - for them to chew on.
Ultimately the passengers are safe, the aircraft's secure on the ground and I've written/am writing the report(s)....what's your problem??
Cheers.
A significant challenge for creating this NNC is to come up with "memory item" pitch and power settings that work for all aircraft and all flight regimes. Presumably, MCT and 15 degrees does not work for all aircraft and all conditions. The tab data is limited, but the go-around chart suggests that for certain aircraft at heavier weights and high density altitudes (e.g. Mexico City), 15 degrees pitch would be too high. I suspect it might also be unsuitable for a heavy-weight, Flaps 25 takeoff. At the other end of the spectrum, a light-weight low density altitude scenario may result in a flap overspeed.
Keep in mind that once the initial steps have been completed, the crew should then move on to the expanded NNC. Step 7 of this checklist directs the crew to the tab data to obtain the appropriated pitch and power settings for their aircraft and conditions. If executed correctly and promptly, then it shouldn't take long before the aircraft is configured for a safe climb to MSA.
I would caution against intentionally disregarding the steps of an established NNC procedure. It's one thing to decide that a certain NNC does not fit a certain situation. It is entirely another to make up your own procedure. Don't expect your flight department or certificate authority to take such a casual attitude when they review your actions.
That said, I have three concerns with the current Airspeed Unreliable NNC procedures as they apply to takeoff (particularly when accompanied by a false stall warning). First, there is no clear guidance on when to retract the flaps. Second, there is only limited information in the NNC regarding erroneous system effects at either the low-speed (stick shaker, EFSM, STS stall ID, autoslats) or high-speed (overspeed clacker, flap load relief) regimes. Third, flight crews are not being exposed to this malfunction on a regular basis in the sim. It can be challenging situation to handle, but really not much more than an takeoff engine failure. The difference is that we practice one all the time, the other not so much.