Authoritative HSI Techniques

[PBlank]

Is there a written and definitive text on the proper usage of an HSI?

Here is an example: Imagine you are tracking inbound on the 270 degree radial. You would have the HSI course selector arrow set for 090 and the TO arrow pointing ahead of the aircraft. Your 'clearance' is to fly to the VOR and turn right and track outbound on the 180 degree radial. I know many folks who, upon arriving at the vor, will set 360 degrees into the HSI course selector and 'fly the tail'. I also know folks who like to have the head of the needle match the heading of the aircraft and they put the needle head at 180 and have the 'from' flag showing.

I have tried to find a 'definitive' and 'authoritative' discussion or written document as to which technique is the officially sanctioned one but I have been unable to find it. I also tried to research who invented the HSI thinking that they might have published something.

I understand the pros and cons of each method...I am just trying to find something official to hang my hat on (so to speak).

Thanks,

Phil

[STBYRUD]

On a proper HSI? My 'authoritative' answer: Set the course, fly the course. Thats why its called a course selector. If you don't then you will fly away from the arrow, why would you want to do that?

[eckhard]

Well actually on an HSI you won't have opposite indications but I agree, set the course and fly the course!

[STBYRUD]

Doh! That was really poorly worded on my part... Well eckhard, of course, there is not really an opposite indication, but flying away from the arrow is contradictory to my logic, but sure, it always shows you the correct direction to turn to correct an offset.

[eckhard]

I once planned to depart a grass airfield on RWY 06, made all the correct 'all stations, traffic information' calls, lined up and took off, turned downwind and found myself heading 060!

You are absolutely right, logic sometimes turns things on their head!

[PBlank]

I appreciate both of your responses. I have heard pros and cons both ways but it appears that there is no definitive text on this subject.

Thanks,

Phil

[STBYRUD]

Text? Oh no, I guess that falls in the mysterious field of 'technique'.... ;)

[eckhard]

One further consideration is that if you plan to fly the HSI indications whilst coupled to a Flight Director or Autopilot, you probably should set the course that you plan to fly (180 with a 'from' flag in your example).

The reason is that most auto systems that I've seen would have trouble interpreting the electronic signals from the beam bar deviation and supplying a sensible correction if the aircraft heading was more than 30 or 40 degrees from the desired course. The systems can cope with a bit of drift but 180 degrees may be asking a bit much.

Of course, our clever human brains have no trouble in doing this, which is one reason why we are still employed to sit up front (thank goodness)!

[aterpster]

PBlank,

I appreciate both of your responses. I have heard pros and cons both ways but it appears that there is no definitive text on this subject.

First time I've heard of pros and cons on this subject. VOR procedures have had system tolerances (flight technical error) evaluated and procedures developed over the years on the premise that the course deviation indicator CDI would be used for radial tracking.

RMIs have issues that make them suitable for reference but not for VOR radial tracking.

What does the autopilot used when engaged in nav mode?

[Big Pistons Forever]

PBlank,

RMIs have issues that make them suitable for reference but not for VOR radial tracking.



There is no reason a an RMI can not be used for tracking a VOR radial. It is usually not required because you can just follow the track bar, but on one aircraft I fly the Capt has Nav 1 on his HSI and Nav 2 on the RMI and the FO has Nav 2 on his HSI and Nav 1 on the RMI.

On an approach which has a VOR radial as a transistion to the IF I set up the track bar for the approach well back and finish tracking to the IF using the RMI.

[Intruder]

First time I've heard of pros and cons on this subject. VOR procedures have had system tolerances (flight technical error) evaluated and procedures developed over the years on the premise that the course deviation indicator CDI would be used for radial tracking.

RMIs have issues that make them suitable for reference but not for VOR radial tracking.
If you routinely use your crosscheck and backup instruments, then you will not be looking at an unfamiliar panel or struggling to even set it up if your primary instrument fails. I have flown (and been evaluated on) MANY VOR (or TACAN) and NDB approaches, including to aircraft carriers, using only an RMI for course guidance. It can be done within approach tolerances if you practice regularly.

It is no different than the automation/hand-fly argument. If you think you NEED an Autopilot or Flight Director or CDI or HSI to fly the approach, then it is likely you will not be able to to fly one without the instrument. OTOH, if you practice regularly in ALL available modes, then a simple instrument or system failure will not turn into an emergency procedure...

[aterpster]

Big Pistons Forever:

There is no reason a an RMI can not be used for tracking a VOR radial. It is usually not required because you can just follow the track bar, but on one aircraft I fly the Capt has Nav 1 on his HSI and Nav 2 on the RMI and the FO has Nav 2 on his HSI and Nav 1 on the RMI.

I am well aware it can be done but there is a good reason not to be doing it, at least when circumstances are critical, such as on a VOR instrument approach's final approach segment. The FTE assumptions used to provide protected airspace for a VOR IAP's final approach segment does not make allowances for the additional FTE that results from using an RMI instead of the CDI.

Because of the simplistic manner in which VOR IAPs are constructed, there is a geometric pad unless the final approach segment is at the maximum permitted distance from the VOR facility.

All the air carrier aircraft I flew had dual pointer RMIs for both pilot positions. We used them only for reference with VOR, but they were primary for NDB IAPs. NDB criteria make allowances for the use of an RMI and, for that matter, a fixed ADF compass card.

[aterpster]

eckhard:
The reason is that most auto systems that I've seen would have trouble interpreting the electronic signals from the beam bar deviation and supplying a sensible correction if the aircraft heading was more than 30 or 40 degrees from the desired course. The systems can cope with a bit of drift but 180 degrees may be asking a bit much.

I believe you're thinking in terms of a localizer, where the course window (aka, OBS) only references a HSI to the correct position, but absent that the localizer deviation will still be correct, albeit offset and confusing. With VOR, though, the actual track deviation will be in error with an incorrect value in the OBS. (The OBS may be a numerical value window, or simply a movable arrow in the "cheaper" HSIs.)

[Spendid Cruiser]

I know many folks who, upon arriving at the vor, will set 360 degrees into the HSI course selector and 'fly the tail'.
I don't understand why anybody would "fly the tail". Try doing that on an ILS, it clearly isn't the way it was intended to be used.

[hikoushi]

Flew the Dash-8 for years, and that autoflight system will track whatever is under the head of the needle in VOR mode. The needle is your way of "talking" to the AFCS and telling it which way you would like to go. If you set the "tail of the needle" to your planned VOR course on that type of system, your autopilot will take you in the direction it thinks you want to go, which is towards the head of the needle.

Could be bad if there is a mountain that way.

Used to fly lots of procedure turns, etc. in that aircraft and the needle always pointed in the direction we actually wanted to track the course ("Turn, Time, Twist, Throttle, Talk", etc.). If you are not currently flying an aircraft with this type of AFCS but expect to at some point in the future, it would be a good idea to avoid building a habit pattern that could cause a negative transfer of learning as you transition later on.

Current A/C is all about the magenta line, so these skills are fading fast. X-Plane helps keep the memory sharp, though, I tell you!

[Microburst2002]

Boeing had a text about HSI and RMI use, very nice.

I think it was Boeing...
Anyone of you, "veterans" remember it?

[Sciolistes]

How about the FAA Instrument Flying Handbook:
The desired course is selected by rotating the course-indicating arrow in relation to the azimuth card by means of the course select knob. This gives the pilot a pictorial presentation: the fxed aircraft symbol and course deviation bar display the aircraft relative to the selected course, as though the pilot were above the aircraft looking down. The TO/FROM indicator is a triangular pointer. When the indicator points to the head of the course arrow, it shows that the course selected, if properly intercepted and flown, takes the aircraft to the selected facility.

When the indicator points to the tail of the course arrow, it shows that the course selected, if properly intercepted and fown, takes the aircraft directly away from the selected facility. The glide slope deviation pointer indicates the relation of the aircraft to the glide slope.

[eckhard]

Hikoushi,

If you set the "tail of the needle" to your planned VOR course on that type of system, your autopilot will take you in the direction it thinks you want to go, which is towards the head of the needle.

Could be bad if there is a mountain that way.

Thanks for explaining more clearly the point that I was trying to make earlier.

Sciolistes,

As usual, the FAA keep things simple and therefore clear and easy to understand. A good explanation of the correct technique.

Eck

[PBlank]

Just wanted to say thanks to everyone who replied. I was able to find out that it was Collins who appears to have invented the HSI but they did not include any operational data per se. The info above (about autopilot) was very insightful -

Thanks again,

Phil

[A37575]

Current A/C is all about the magenta line,

I quite often see pilots flying a holding pattern magenta line by using the heading select mode and carefully running the aircraft along the magenta line like tracing paper and pencil. Is this a valid technique?

[Denti]

Sounds a tad weird. If the magenta line's there why not let the automatics follow it on its own? If it does it correct that is, there was a known bug in one of the 737 FMC updates that calculated and traced incorrect holding patterns which surprised you halfway through straight on the line with the message UNABLE HOLD AIRSPACE.

So crosschecking it with timing and a tuned navaid (if the fix is based on one) is still a mighty good idea.

[BOAC]

Is this a valid technique? - either extreme boredom or some attempt to retain marginal flying skills?:)

[Microburst2002]

PBLANK!

Now I remember an excellent, excellent manual that most of the brits here surely know well.

Trevor Thom's Private Pilot Manual has a volume on Instrument Flying and Radio Navigation. It explais it all with lots of graphs.

The best way to use the HSI and RMI is to turn the instrument into a map, like a "mental ND". You can do that if you ignore the little airplane in the middle of the EHSI and think of your airplane as being in the tail of the needle.
Then you have your situation in relation not only with the navaid but with anything else around it (rwy or whatever).

the boeing document I mentioned recommended the same technique

[aterpster]

A37575:
I quite often see pilots flying a holding pattern magenta line by using the heading select mode and carefully running the aircraft along the magenta line like tracing paper and pencil. Is this a valid technique?

Most, if not all, modern FMSes have a hold mode where you can construct the required holding pattern then let the automatics fly it with positive course guidance all the way around the circuit.

If not, the magenta line's viability for manual flying depends upon the map scale set. It's far better to use the "OBS" mode (which has various names) and select the inbound holding course so the deviation indicator can be used for the inbound leg of the pattern.

[PBlank]

Thanks for the info!

BTW, do you know if the Boeing document is pubished anywhere? I have done a couple of web search and have not been able to find it.

Thanks again!

Phil

[Idle Thrust]

I agree with all who say set the course you wish to fly. There is an exception and that is when flying a Back Course ILS - then you must set Front Course inbound track in order to avoid the reverse sensing of a back course signal.

Not sure how many Back Course approaches are left (they used to be quite common in Canada) and glass cockpits coupled with "BC" switches have probably rendered this a moot point.

[Microburst2002]

Sorry.

Probably it is not available in PDF, I had it on paper many years ago. The graphs used the typical HSI and RMIs you could find in any non glass cockpit airliner. It must be an old document. A retired pilot handed it to me.

I can't find it and scan it because it is far away, in my homeland. If I ever find it and have time, I will scan it.

But you can purchase Trevor Thom's Instrument Flying and Radionavigation. It is still published, I think.