The Pilot Viewpoint

[500AGL]

Since I brought it up in another thread, I thought I’d share the photos I snapped of flight data the other day, to send to pilots and budding pilots as an exercise.

The photos represent a scenario where something is wrong, and two of the photos provide all the data needed in each photo to explain the situation, but to go easy on my friends I sent them all three. You always use all the resources you have to determine the correct answer to a problem.

If it’s obvious to you maybe hold off on answering, but I encourage those that may not know to look at all the data and take a shot of explaining what is wrong.
This is for fun, and perhaps someone can learn what they've not seen before.

[kestrel]

ooh! ooh! ooh! Pick me! Pick me!

[500AGL]

While Kestrel doesn't count, I'll break it down quick for anyone that had a curiosity.

Let's look at each photo.
IMG_6739.jpg

I like this on first, for everyone has an Airspeed and everyone has a Tachometer.
In this case I have a tach and a manifold pressure, and fuel flow.... so even more data.

Airspeed is 50-ish, and engine is 23 squared? Wait, what? How does that happen? Well, you could be climbing. But, you have a big windshield and it's obvious you're not climbing (take my word for it).

So level flight, unless you lost the outer 40% over your prop blades, or your towing a couple gliders, your engine is turning rpms to make cruise power.
Fuel flow also shows it.
You also have your hearing to help prove that your engine is turning that rpm, so it's likely that the engine info is correct.
In this case we also show CHT/EGT to further quantify power.

So, the Indicated Airspeed must be wrong. Why would it be wrong?
- Loss of pitot pressure
- Loss of static pressure (Sidebar.... if the static pressure is clogged, how is the IAS affected?)

Note, there is also an IAT - Inlet Air Temp in that JPI 730, that is showing about -7 degrees.

[500AGL]

IMG_6738.jpg
Photo two, which is can be argued as the best one, but in reality the previous two gauges provide more quantifiable data.



Airspeed - 55
Attitude - level flight
Altitude - 1340, but also note the VSI needle is zero, again, level flight.
Tailwind - 64 HA! What!?! 64 mph tailwind? Cool...
Groundspeed - 115 - Well, sure, 55+64= 115 right?
TAS - 54 - non-factor
OAT - 9 degrees F. Yep, that's sorta cool out.


So, you're not climbing but only going 55 through the air. With a 64 mph tailwind. Wow, crazy right. First thing you have to say is "what's the likely hood of that really happening". Since it's not, what's causing it? Well, your engine sounds the same, you're flying level, your controls feel the same, so that airspeed can't be right.

How does electronic instruments determine where the wind is coming from? Math. It looks at your IAS, your GPS derived groundspeed, your flight path/heading, and the outside temperature. Then says if you're only going 55 through the air, but your speed over the ground is 115 in the same direction as your path, well obviously 115-55 = 64, so you have a 64 mph tailwind.

No Virginia, that's a lie.

The pitot tube is partially clogged, so you only have enough air pressure to indicate 55. Therefore, the math is right but it's like old computers - bad data in equals bad data out.

[500AGL]

And photo three, is just a confirmation that the other data is on point.

IMG_6740.jpg

GPS Groundspeed is the same. The truths in this case are GS, RPM and MAN. Well, and ice. Definitely ice.

[predragvasic]

The EFIS screen gave us all the info we needed to figure it out. The massive discrepancy between IAS and GS, low altitude, OAT below freezing all point to a single culprit (pitot tube).