I’m looking to upgrade my panel. Right now, I’m a /u. If all goes well with my annual coming up in November, I’m planning on treating myself to some new equipment. In moving to a modern panel, I think the first thing I’d like to start with is a compass slaved HSI. I believe that would give me the most bang for my buck. I’m not looking for one that will give me an electronic display of course, traffic, etc. I want to keep it simple: Slaved for good heading information, vertical and horizontal guidance, and the ability to get information from the NAV radios or a GPS (probably a Garmin 480) installed at a later date. Any thoughts or recommendations would be appreciated.
RJF, N8052R, 1970 Sierra
Everyone has their own opinion on HSIs. Traditional flyers with traditional panels always consider them to be worthwhile. In the homebuilt community, where the thinking tends to be more progressive (since the equipment can readily be more progressive), almost no current builders spend any money on an HSI anymore.
My personal opinion, having been in both camps, is that HSIs are now virtually obsolete. The only significant reason for using an HSI now is if you need to combine a VOR-LOC-GS display with the DG to save the “hole” for something else. Here are the reasons I say this.
The primary purpose of an HSI was to create a better, more intuitive, situational awareness, by displaying the plane’s heading relative to the VOR radial or Localizer beam being used for navigation. Of course, you had to get used to it first.
An IFR panel mount GPS, or even a handheld GPS, provides so much more situational awareness, that an HSI’s presentation pales to insignificance. The IFR GPS also makes it easy and legal to file “Slant Golf”. Depending on where you live and where you travel, being able to file Direct to most destinations can save significant time and fuel. Since we went Slant Golf with a 430 in our Sierra, back in April of 2000, every IFR flight plan has been filed Direct. Not more than a dozen flights have been issued on-airway revisions mid-flight, and we have been through the country coast to coast, and through southern Canada, since then. Most reroutings were down around Orlando, or up around Charlotte. Even if a route revision is issued, the GPS makes it so simple to dial in the initial waypoint and head that way, while you dope out your new route.
If you later install a panel mount GPS, conventional HSIs probably won’t qualify as the required course indicator and annunciator device. One of the electronic HSIs might qualify, depending on the HSI and the GPS. They cost big bucks.
Having the slaved compass function is a nice touch, to eliminate manual DG corrections for precession. Is that enough of a convenience to spend the money on that, rather than on an IFR GPS? You can get a used 430 put in now for what an electronic HSI used to cost. Even used 530s are out there at bargain prices, as people step up again. If you can possibly swing it, I strongly recommend the 530 over the 430. I say this because the effective map area is nearly twice as large, once data blocks are considered. The extra map area allows things like terrain and lightning to be displayed without having to change pages.
Precession correction, other than for reversion to backup, becomes a non-issue if you have (for example) a 430 and a coupled autopilot. This is because the GPS will guide the plane on the great circle route, within a matter of 20-30 feet of course centerline, no matter how the wind shifts or how the DG precesses. Even without the autopilot, the GPS course deviation indicator will show needed course heading corrections, regardless of the DG heading or precession errors. I’m not advocating flying without making corrections for precession; I’m just saying you gain no operational advantage from a slaved HSI, if you have a good panel mount GPS. You just need to be prepared to fly in backup mode if needed.
So, my suggestion is to skip the past “norm”, and go full speed ahead with a good panel mount IFR GPS as soon as you can.