Partial Panel Failure

[Jaybird180]

Im looking for an interpretation of this scenario and how to deal with this. It is totally fictitious. I thought about this after reading an accident investigation during a missed approach.

Scenario:

Instrument rated pilot decides to get some practice in actual conditions and is carrying 3hrs fuel in the Single Engine round dial airplane. Departure point is CAVU and IMC airport where the approaches will be flown is 1 hour away (headwind included).

After 3 good approaches the pilot decides to get 1 last approach in before heading back, considering fuel reserves.

During the approach, the pilot notices that the GPS derived advisory glide slope needle continues to fall below, the lower he gets on this final non-precision approach. MDA for this hypothetical is 400' AGL at the high DA airport. Last approach, breakout was about 430' and the advisory glide slope he is following will simulate a precision approach by colocating the MAP at 400' AGL.

The pilot is aware of the terrain to the left and right of the runway, that there is little margin for error (about 1.0 miles either side of the runway). The approach is flown at 90kts.

As the airplane descends, the pilot becomes increasingly concerned about continually chasing the GS needle and it seems the weather conditions and winds have changed. Breakout occurs at 410, with the GS needle 1 dot low and the missed procedure is initiated.

Power is increased, but the climb performance is more anemic than the last approach.

As the pilot goes back into the soup, he notices the DG turning to the right. The scan of AI, TC and inclinometer indicate S&L flight. The wet compass agrees with the DG, as it is changing heading by turning to the left.

What's going on here and what action should the pilot take?

 

[Jaybird180]

Also, assume no Synthetic Vision or EVS in the airplane.

 

[Jaybird180]

Correction: Not S&L flight. AI showing wings level, >+10 nose up, VSI 20fpm climb, ASI is at Vx.

 

[TMetzinger]

What's the Outside Air Temperature?

Also, don't tell me which way the DG and compass dials are turning... tell me if the heading is increasing or decreasing... depending on the type of compass this matters.

Edit... since this was an RNAV approach, what was the GPS groundspeed? I'm suspecting a change to a tailwind, and the difference between TAS and GS can confirm it.

Also, since there's advisory vertical guidance, we should be able to assume WAAS and SBAS, meaning the GPS guidance is trustworthy.

 

[Jaybird180]

What's the Outside Air Temperature?

I don't know enough about instrumentation failure to know how to answer that. So, I ask you how does OAT affect the gauges or what they're telling you?

Also, don't tell me which way the DG and compass dials are turning... tell me if the heading is increasing or decreasing... depending on the type of compass this matters.

They agree on direction. The numbers are getting higher.

...since this was an RNAV approach, what was the GPS groundspeed? I'm suspecting a change to a tailwind, and the difference between TAS and GS can confirm.

that's what I was implying....setting the stage

Also, since there's advisory vertical guidance, we should be able to assume WAAS and SBAS, meaning the GPS guidance is trustworthy.

Ok. Any concern for CFIT? How about unusual attitude?

 

[TMetzinger]

OK, if it's below freezing, I need to suspect my pitot and possibly my airspeed indication... I also need to be concerned about a static port freezeover, if I was in cold clouds. I have to be worried about ice and it's effects on the wings and engine

Basically, is my crappy climb performance due to ice on the airplane or intake manifold? Do I have an instrument problem?

According to what you've told me my AI is indicating a climb without any bank. My TC is not indicating any turn. My DG and compass are indicating a turn but they don't necessarily agree, if the DG is showing a turn to the right (values increasing) and the compass is also showing a turn to the right (values increasing).

At this point, I don't know what to believe. If I'm actually turning, the TC and DG should agree.

I suspect that perhaps my TC is bad, but if it is it SHOULD be flagged - there's a reason that instrument has a flag on it.

What's my airspeed indicator doing? That matters and is a clue to finding out what instrument is lying to me.

Right now, among the three gyros, the one that disagrees is the DG, it shows a turn while the TC doesn't, and the AI shows wings level. I'd assume the DG lying to me IF the compass wasn't agreeing with it. Now the compass may be swinging due to acceleration on the missed approach. So at this point I need to wait another few seconds to see what changes, if anything.

VSI is independent of wind, so regardless of what my climb angle is in relation to terrain, if I'm at the correct pitch attitude, if I'm getting proper performance out of the engine, and if the wings are clean (of ice AND in the proper configuration), I should be getting "normal" climb performance relative to the AIR (not the terrain). Yet you seem to indicate I'm not.

 

[Captain]

Can't happen IRL without multiple failures.

DG and Mag Compas turning with AI, TC showing wings level (albeit in a climb) mean two instruments are acting erratically. That's a multiple system failure and that will kill any pilot. I'm for a vacum failure affecting the DG and AI. Or an electric failure affecting the TC. Or a pitot failure affecting the ASI, ALT, VSI. But crossing systems isn't likely.

Btw, I'd go with Tim's acceleration on the missed causing the Mag error, except there is very little acceleration going on. Ref to Vy is a very small change relatively in any plane I can think of.