Thursday, August 25, 2016

Partial Panel

Flight Data

Airplane: Piper Cherokee PA-28-161/A N9206N

Hobbs: 1.6

Landings: 1

Instrument Approaches: 3

Flight Overview

Today was partial panel work. The plan was to fly the following approaches: Oceanside VOR missed, Carlsbad ILS missed, Montgomery Field ILS full stop.

During the flight to the first approach, Oceanside, I was expecting that my instructor would introduce a partial panel situation. 

What is Partial Panel?

Partial panel is a simulation of the loss of flight instruments associated with loss of vacuum. The airspeed indicator and attitude indicator become inoperative as a result. The intent is for the student to demonstrate his or her ability to perform flight with less than a full complement of flight instruments while in instrument flight.  The instructor uses a cover which has suction cups attached to it in order to hide an instrument from the student. The student must compensate for the loss of instruments by using other instruments in the panel.

Executing the Partial Panel

We were approaching the Oceanside VOR from the south somewhere close to the V23 airway. I was expecting we would go partial panel at some point prior to crossing the VOR. At the VOR, the approach can be performed by doing a teardrop entry. The holding pattern inbound leg is 90 degrees, the outbound 270 degrees. Approaching from the south, the procedure would be, upon positively passing the VOR, turn left to a heading of 240, fly 1 minute, then turn right to intercept the 90 degree radial to the VOR and complete the approach. 

VOR Approach, Oceanside

Prior to arrival, we were advised that we would be number 2 for the approach and to expect a hold. That added a wrinkle to the process. My instructor decided not to put me into partial panel mode as a result, doing an actual hold is rare and I suspect he wanted to give me that experience without overloading me with the burden of doing it partial panel. However, we were given a descent to 2500 feet and it was obvious that we would not hold, so my instructor hid both the attitude indicator, and the heading indicator.

It's hard to be sure exactly how I dealt with this. I did well enough, plenty of experience scanning instruments over the years probably accounted for the bulk of my approach to compensating. I do know that I replaced the attitude indicator with the turn and slip indicator plus mag compass for turns. As far as the use of the attitude indicator, I suspect scans of airspeed indictor, rate of climb indicator, turn and slip indicator, and altimeter all came into play.

We basically found the field, and the missed approach point, and the panel instruments were uncovered.

Compass Errors

Here are some memory aids about compass errors that I picked up during the preflight discussion:
  • ANDS - accelerate north, decelerate south. On a west or easterly heading, accelerating will cause the mag compass to show a turn to the north, and decelerating will cause the mag compass to show a turn to the south.
  • UNOS - For turns of 90 degrees or more from a west or east heading, undershoot when turning north, overshoot when turning south. How much depends on the latitude where you are flying. Given I am flying at 32 degrees north latitude,  the undershoot or overshoot amount for a 90 degree turn would be equal to the latitude, or about 30 degrees. For less then 90 degrees, interpolate - e.g., 45 degrees would be half, so the amount to undershoot or overshoot would be half of my latitude, about 15 degrees. Yes, at the equator, there is no need to compensate. And things reverse in southerly latitudes. The following video illustrates this:

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