Avionics upgrades and roll rate

By Ian Andrews

Many of us are currently going through the process of upgrading our avionics as the old analogue stuff wears out, or we want a flasher looking instrument panel.

The logical approach is to go for solid state equipment that replaces either all or some of the old six pack round dial instruments. Only a handful of you will be IFR but we all rely sometime on what is in front of us in the way of our Artificial Horizon (AH) and Direction Indicator (DI) – put simply, the two instruments in the middle of the six pack (image, top right).

To upgrade your cockpit you can replace these two with an Aspen, as shown in image 2; or just the AH with a Garmin G5 or Dynon D10 (image 3); or you can go for the deluxe version using all Garmin gear (image 4).

I chose to refit with the full monty of a Garmin G500 replacing the six pack, but keeping old standby Speed, Alt and an AH driven by vacuum, as required by law. It is a good set-up and provides a great multi-functional display in the right screen while showing the entire six pack on the left.

From the very first flight I struggled with the indication I was getting, and had to adjust my thinking to comply with what was for me an unusual depiction of my roll rate. However, I could not really put my finger on what was upsetting me and put it down to getting old and being a tad uncurrent.

For those not familiar with the terms, at the centre top are two triangles. One points down and is called the ‘Earth Pointer’ while the other points up and is either called the ‘Sky Pointer’ or the ‘Roll Pointer’. This is the term I was trained on 25 years ago, when I was also trained to check my roll rate (= angle of bank) as part of my scan.

The roll pointer always showed my rate of turn which, in image 4, is about 2 degrees (yes, I am out of balance). I would have said 2 degrees roll to the right and would have rolled left to align the two pointers, but look at the wings on the horizon. I need to roll right to level them, which to my mind was confusing. I learned to live with it. Simple: just put the earth pointer over the roll pointer. However, it did not feel right in my brain.

About a year after doing the upgrade I fitted a new Garmin GFC 500 Autopilot (AP) which needed a Garmin G5 to drive it (don’t ask the cost). Now I could get rid of the vacuum AH and remove the vacuum system because I now had an electronic backup with four hours of standby battery.

The AP is a fantastic piece of kit that has taken IFR flying to a new level of ease. A glide path at every airport based on the GNC650 GPS receiver. It can fly the enroute, STAR with a hold, approach with advisory glidepath, absolutely hands off down to the missed approach (MA). Then I just hit a go around button and all I have to do is add power because it pitches up, unsuspends the GPS and climbs away on the MA track. All I do is monitor the process and be ready to step in if it is not correct.

I was out flying for fun a few weeks ago and was doing some steep turns just to check everything was working when I noticed a discrepancy between the G500 and the G5. Look at image at the right and compare the two roll pointers.

The G500 has the roll pointer to the left and the G5 has the roll pointer to the right. I know I have to roll my wings level by turning left because the horizon tells me that, but my brain is saying turn right on the G500 and turn left on the G5. It is the G5 indication that I am used to seeing on the old instruments and that I am comfortable with. How did this happen?

I researched it and a study done in Sweden gave me the answer. Three settings are used in the avionics world. General Aviation (GA) uses the roll pointer to show the angle of bank, as per my G5, with the roll scale slaved to the horizon. Commercial Jets do the opposite and slave the roll scale to the wings, as is shown on the G500. The other way is a military style where the roll pointer is at the bottom, but that’s not relevant here.

This article was commissioned as there have been a few accidents caused by turning the wrong way in IMC and losing control of the aircraft. The problem has been recognised for many years, so why did my aircraft have the two different settings on the one panel? I guess they were installed at different times, but someone should have checked.

It appears that the G500 comes out with the ‘commercial’ default setting while the G5 comes with the ‘GA’ default setting. No-one looked at it and I was not pushy enough in the first place when I felt uncomfortable with the G500 display.

It has now been fixed, and what a difference in my brain! The set-up is now logical and reflects the way I was trained. Of course, the wonderful autopilot never overbanks past a rate one turn, so it’s easy to overlook that, but when you were trained on hand flying without an autopilot, you use every indication you can get in the scan.

Let’s be honest here. This is a known killer. The Swedish study has shown that experienced pilots failed five times more often with the commercial set up than with the GA one.

I have raised this with CAA and several Avionics shops, who will be taking a closer look at what they do in future. It is up to you to speak up if you find it uncomfortable in the transition from analogue to a digital, technically enhanced cockpit. I am glad I was not in IMC when I started the transition, and I am also glad I have been able to do lots of practice since.

By the way, I do not fly IFR these days as it is not permitted on the new DL9(P) medical. I do go with an instructor to keep my skills up, and I look forward to getting IFR on the DL9(P) soon, IFR being so much safer than scud running when you’re flying from A to B – and it’s a lot more relaxing too.

This article first appeared in the Spring 2021 edition of Approach Magazine, the dedicated magazine of AOPA NZ, which is published quarterly.