Teaching Partial Panel on Glass

In the past year I’ve been lucky enough to have acquired a decent amount of experience in G1000/GFC700 Equipped aircraft. One of my customers purchased a G1000 equipped Bonanza late in 2010 and his insurance company required he undergo a quantity of dual prior to being able to solo the craft or carry passengers. Fortunately, I was the instructor he chose to use and over a year together we flown a considerable amount of time both VMC and IMC , in all manners of airspace.

Fast forward through that time and I found myself preparing a few pilots for their Instrument Practical Exam. For those unfamiliar with the rating requirements, an element of the practical test standard requires the applicant to demonstrate ability operating the aircraft partial panel

Devising a plan to meet this requirement posed some interesting questions. What constitutes partial panel in a glass aircraft and what are we trying to teach/demonstrate when flying partial panel?

Instrument crosscheck, reading, interpreting and verifying that the flight instruments display correct indications, without ambiguity, are the primary skills taught to pilots during their instrument training.  In a glass airplane, attitude and direction is the product of the AHRS or attitude heading reference system. Airspeed and altitude are devised from the ADC or air data computer.  These devices are backed up by a conventional altimeter, airspeed indicator and an electric attitude indicator. If the AHRS unit were to malfunction in flight the pilot then would transition to the backup instruments for attitude altitude and airspeed while utilizing the navigational system data depicted on the multi-function display for position information.

While this, by no means is an easy task, redundancies mandated by the FAA place these backup instruments on the panel to provide the pilot with the critical flight information required to assure the desired outcome safely.  As glass cockpits are relatively new to piston powered general aviation aircraft the documentation available to the applicant, instructor and designated pilot examiners on what is considered a failure and guidance on how to simulate one is scarce.  

Simply dimming the display can be used to simulate the loss of a primary display unit but this leaves the pilot without any navigation information. Additionally, in the real world, if the display unit were to fail, pressing the big red display backup button on the bottom of the audio panel would put the system in reversionary mode and light up the MFD, with the PFD’s data.

I had a conversation about that with our local DPE and his response was “he’s got to play the game”. I understood this to mean that the applicant would forgo the actual display failure procedure and fly NAV data off of the NAV Range ring and the track vector on the MFD while using the conventional instruments for attitude altitude and airspeed while the PFD was dimmed.

Pulling the breaker on the AHRS is a more accurate method in my mind of demonstrating partial panel as this provides a more conventional, gyro’s failed experience. When the AHRS is failed the attitude indicator and the HSI display bright red X’s . However the NAV portion of the HSI still displays the course deviation indicator and its deflection off of the chosen navigational source. It also makes the applicant divide their scan across the panel. Failing the Air Data Computer (ADC) by pulling the breaker is really a non-event as we have the airspeed and altitude directly readable off the standby instruments. Additionally most pilots flying high performance aircraft typically fly defined power setting that produce specific airspeeds. More noteworthy is pulling the ADC breaker will eliminate the Mode C data required by the transponder- a big drawback in these parts with the New York Bravo a scant 15 miles away.

To me it seems that the primary difference and difficulty in flying partial panel on glass is the lack of the turn coordinator. The attitude reference in the glass airplanes has the pyramid shaped pointer at the top of the display. The base of the pyramid represents the ball while the top details the bank angle. If the base is off center to the pointer “stepping on the base/ball” coordinates the turn.  The HSI indicator has graduations on either side of the lubber line to determine rate of turn, the closest mark represents half standard rate and the second mark is standard rate. While maneuvering a magenta arc moves through these graduations to detail to the pilot the rate of the turn.

With the display or AHRS gone the rate and quality of the turn information goes away as well. This leaves the pilot somewhat unable to perform standard rate turns which makes turns to headings more difficult especially in the  vectors to final situation one would likely be in if the equipment checked out in IMC. Most of the bigger airplanes are now adding redundant AHRS and ADC units to their glass implementations. Maybe one of these days there will be no partial panel, but until that occurs we’ll have to keep teaching and evaluating pilots skills flying it.