Using GPS ground speed to resolve Unreliable Airspeed
 

Personally, I'd stick with the approved procedures for unreliable airspeed.

Your GS is 500kts. Are you safe? Could be TAS of either 650 or 350 with a 150kt wind. Neither of which will keep you flying for long at cruising FL.

Well, I've had my airplane flying 11 MPH backward, according the GPS groundspeed (It was a windy day), so with that in mind, I'll continue to use the airpseed indicator for airspeed information.

I do remember test flying a Tiger Moth following maintenance. It had three airspeed indicators, one in each cockpit, and a vane device on the wing strut. They all differed by about 10 MPH to each other, so I ignored them all, and just flew by feel, it was fine. In hindsight, I think the vane on the wing seemed the most accurate.

I really like the GPS for pointing me home, and telling me when I should expect to be there.

Hang on. Nobody is suggesting you suddenly find yourself plopped into a scenario with now idea how you got there or what the current conditions were and now had use the GPS.

You will obviously be happily flying along, knowing you are doing the right speed, then the pressure instruments go awry. The GPS GS is a great indicator in that case to keep you flying until you descend or otherwise sort out the problem.

The other scenario is after takeoff. You are starting from a relatively accurate known point: get it cleaned up and maintain 250 GPS GS, allow for the low level wind if you like. Safe as houses.

GPS GS is a fantastic aid if you have no IAS. You could even use your phone GPS speed.

In my aeroplane, the FPA is not reliable during a UAS event. I assume that AOA (unless it was just a raw readout from the vane) would also be dodgy.

What's wrong with the tried and tested method of: "The correct attitude + correct power setting = correct speed?"

Having said that, at very low speeds landing away from an airfield (helicopter) I monitor the GPS groundspeed against the IAS to determine/confirm into wind or downwind on the approach.

In your 737 at 40t or your 737 at 60t, if you set your UAS parameters at slow speed or high speed the speed outcome will be completely different.

And yet, it's safe, which is what matters in the end, not how accurately you can fly the speed you can't even see or whether you will climb or descent.

This is Boeing's take on this:

If installed, AOA readout normally is directly from the vane.

But aren't pilots paid to know the difference?

Let me guess, a luddite that has never actually tried a full-blown "I have no idea what my speed is" approach?

You lot should try to fly an approach in a jet based solely using the speed/power/attitude tables. Then fly it using the GPS speed and the wind from the tower. Chalk and Cheese.

Not IMO. Those numbers and procedures are obviously designed for the heat of the moment to prevent you from stalling. A light jet at low level will still accelerate quickly at the recommended UAS parameters and could well end up like the Ethiopians. What's your power setting for 250KIAS at low level?

Are you a 737 pilot? Do you know the difference?

https://support.garmin.com/en-AU/?fa...Uv1QyoxITW2vZ6

Flying a circuit on GPS altitude bears no resemblance to "altitude".

Whatever.

I'll use the GPS down final, you use your tables.

My two pence worth if, as I understand it, there's an argument here about setting the gross pitch power Boeing figures vs. "simply" setting well remembered pitch power immediately you recognise an unknown airspeed situation..

As I read it (from our FCTM and other documentation) Boeing's logic behind not wanting ace pilots setting their committed to memory pitch and power figures for, e.g. for 250 knots 'cos they think they are at 250 knots and S&L is because by the time they recognise the situation they might not be at 250 knots and they might not be in level flight....so that's why they came up with the "it's safe" figures

Of course after the trouble shooting is done we usually arrive by way of a checklist to the weight/pitch/ power etc tables and then fly the machine that way.... so eventually you get to use both techniques (and so honour is satisfied, magenta line, old school or both).

Well, I got the impression that the crew of AF447 did get plopped into their scenario without any idea of how they got there. Trucking along for 10 hours straight, do you constantly keep track of your GND speed? It can change with values that exceed your A/C limits or stall speed, over a very short period of time i you are flying close to the coffin corner.

Thats because the relation between FPA (INU/INS), Pitch and AOA is only perfectly constant and reliable in a no wind environment, flying in a straight line (1g). However, the FPA is a very reliable means of showing level flight regardless of the status of the AS indicators.

AOA is raw readout in either units or degrees. It is only dodgy if the vane is broken like on the MAX. AOA is most useful for aircraft where the total mass can vary a lot during flight, since it will always show you how far you are from stalling. Aircraft with AOA indicators normally have a fixed AOA value to be flown during approach regardless of their weight, thereby changing the status of the AS indicator to a B/U instrument only (during approach).

GPS is nice to point you home, give military pilots great weapon precision and such, but my suggestion is always to be able to fly your aircraft via the control and performance concept, as its the only proven concept that will get you safely on the ground. But there is a catch. It requires propper skills and sufficient training, a thing that magenta pilots probably don't have/get.

While AOA is one of the best alternatives, remember that the latest crashes are due to failing AOA sensors triggering the events that end up flying the aircraft into the ground.

The very best alternative is to equip all aircraft with a crazy stupid alternative that is completely disconnected from the aircraft like a Dynon D3 pocket panel and revert back to basic flying skills..

A 737 will go to Vmo at 10deg pitch and 80% N1 with flaps extended? Or 4 deg pitch and 75% N1 in clean configuration? Even at OEW and a bit of fuel to run the engines, I very much doubt it.

Why do you want to fly exactly at 250 KIAS? It is safe, for sure, but so are UAS pitch/power settings.

I would be very cautios when operating the aircraft outside of manufacturer's recommendations and procedures, especially when it directly contradicts them. A lot of work in the aviation industry went into developing robust UAS procedures post AF447, and they are much better now that they used to be. And despite all the media propaganda, I still believe Boeing engineers and test pilots have more (abnormal) aircraft/sim time and know more about UAS than many of us together.

Boeing FCTM says (my bold):
Good luck explaining to a lawyer why your pitch/thrust settings were better than manufacturer approved procedure, if things end up sideways.

Wiggy is correct plus they also state "at any and all weight/altitude combinations, the aircraft will accelerate from low speeds, and slow from a high speeds.... At light weight and low altitude, the true airspeed will be higher than normal, but within the flight envelope ".

Wiggy, I agree.

No, what's the point? When you go UAS, then note your GPS GS. Maintain it until you work out what's going on. If you pull up to 4° and pull the power back to 75% (Flying Stone/737 UAS?) at FL370, you'd better watch that GPS GS closely because it'll be reducing!

Precisely, and where the Ethiopians found themselves immediately prior to the final dive: at Vmo. I wonder what the GPS GS was then...

Just telling you what my FCOM says.

I didn't say anything about "exactly" 250KIAS. 230-270 GPS GS who cares? At least it's not Vmo with full nose down MACS trim while maintaining the UAS "it's safe" memory numbers while your PM comes up with some numbers from the back of the QRH...

I agree. My point is that GPS GS is an invaluable aid while doing that, especially down low on approach or after TO when wind effect is low/known.