who does VOR "calibration" for most accurate VOR approaches?

Hi,
I recently learned that VOR can be "calibrated" or adjusted to take
into account any error discovered at the 30-day check. For example, if
you need to set OBS at 44 to get centered CDI on the 42 radial from VOR
on airport checkpoint, and 219 to center CDI on the 222 radial, then
you record the errors: + 2 TO and - 3 FROM. Then, when flying an
approach, for example, outbound to the airport on the published 250
radial, you turn the OBS to the 250 - 3 = 247 radial and fly centered
CDI for more accurate approach. Sounds good to me and makes sense. Is
anyone doing it this way? Know of any good reference?
thanks
Greg

In a previous article, "Greg" said:
I recently learned that VOR can be "calibrated" or adjusted to take
into account any error discovered at the 30-day check. For example, if
you need to set OBS at 44 to get centered CDI on the 42 radial from VOR
on airport checkpoint, and 219 to center CDI on the 222 radial, then
you record the errors: + 2 TO and - 3 FROM. Then, when flying an
approach, for example, outbound to the airport on the published 250
radial, you turn the OBS to the 250 - 3 = 247 radial and fly centered
CDI for more accurate approach. Sounds good to me and makes sense. Is
anyone doing it this way? Know of any good reference?

As a followup question, if you record a +2 error on one VOR, will get
always get +2 on every other VOR on every radial? I was flying our club's
Lance the other day and it seemed that VOR 2 was quite a bit off - I'd be
right on the airway according to VOR 1, and pretty damn close according to
my handheld GPS, but VOR 2 was a good 10 degreess off. I was flying to
Ottawa and Ottawa has a VOT, so when I was there I tested it, and VOR 1
was off +4, and VOR 2 was +12. I told the club they needed to fix that
VOR 2, and the other Lance flyers said "but when I test them against each
other on the field here in Rochester, they come out the same". Is that
even possible, or are they really mis-reading the OBSes?

I really distrust testing the two VORs against each other, because one
could be +10 and the other +14, and you'd think they were fine and dandy
and launch into IMC.


--
Paul Tomblin http://xcski.com/blogs/pt/
The only complaint I have against WinDoze is that it doesn't always
fail at install time.
-- Mike Andrews

Greg wrote:

I recently learned that VOR can be "calibrated" or adjusted to take
into account any error discovered at the 30-day check.

Really? Where did you learn that? VOR errors aren't like swinging
a compass. Further, the tolerance of the VOR check covers not only
the allowable inaccuracy in the on-board equipment, but the imprecision
in the way you are testing them (this is why they all have different
tolerances) and the inaccuracies inherrent the VOR transmission itself.

If the VOR passes the 30 day check, just use it. Approaches and
enroute navigation is set up to deal with that much error. There's
no way to calibrate the instrument outside a repair shop.

By the way, if your unit doesn't read a reciprocal heading on
the to/from tests you might want to have it looked at. That
almost certainly indicates a defect in the onboard equipment.

Set the OBS to the published radial/course. In the old days
of vacuum tube radios, the tubes would change their tuning
as they got hotter and wore out. Thus the 30 day check
rule. Modern solid state VOR are very stable and once
adjusted are likely to stay within tolerance until they
fail.

The check can and should be more than the check on one
radial. You can check receiver sensitivity by turning the
OBS a full 360 and noting the proper operation of the
TO/FROM flag. Starting with the needle centered, 10 degrees
should give full scale deflection. Then the flag should
begin to change at 80 degrees and be off at 90 and switching
fully at 100 degrees. Check all the way around. An
airborne check 30 miles away from the VOR will detect weak
signal processing that may not be detected in a ground
check, VOT or check on a visual point close to the VOR, such
as a runway threshold that is 5 miles or so.

VOR radials are not always where they seem to be, the FAA
flight checks airways and instrument approaches, other
radials can be off by a substantial amount.


--
James H. Macklin
ATP,CFI,A&P

"Ron Natalie" wrote in message
...
| Greg wrote:
|
| I recently learned that VOR can be "calibrated" or
adjusted to take
| into account any error discovered at the 30-day check.
|
| Really? Where did you learn that? VOR errors aren't like
swinging
| a compass. Further, the tolerance of the VOR check covers
not only
| the allowable inaccuracy in the on-board equipment, but
the imprecision
| in the way you are testing them (this is why they all have
different
| tolerances) and the inaccuracies inherrent the VOR
transmission itself.
|
| If the VOR passes the 30 day check, just use it.
Approaches and
| enroute navigation is set up to deal with that much error.
There's
| no way to calibrate the instrument outside a repair shop.
|
| By the way, if your unit doesn't read a reciprocal heading
on
| the to/from tests you might want to have it looked at.
That
| almost certainly indicates a defect in the onboard
equipment.
|

Greg wrote:

Hi,
I recently learned that VOR can be "calibrated" or adjusted to take
into account any error discovered at the 30-day check. For example, if
you need to set OBS at 44 to get centered CDI on the 42 radial from VOR
on airport checkpoint, and 219 to center CDI on the 222 radial, then
you record the errors: + 2 TO and - 3 FROM. Then, when flying an
approach, for example, outbound to the airport on the published 250
radial, you turn the OBS to the 250 - 3 = 247 radial and fly centered
CDI for more accurate approach. Sounds good to me and makes sense. Is
anyone doing it this way? Know of any good reference?
thanks
Greg

Flight inspection does just that for VOR final approach courses.

There is no FAA-approved procedure for pilots to further adjust for
individual receiver errors. (An IFR approach GPS solves all those
problems ;-)

On Wed, 12 Jul 2006 08:03:09 -0500, "Jim Macklin"
wrote:

Set the OBS to the published radial/course. In the old days
of vacuum tube radios, the tubes would change their tuning
as they got hotter and wore out. Thus the 30 day check
rule. Modern solid state VOR are very stable and once
adjusted are likely to stay within tolerance until they
fail.

Except that back then the rule required that the VOR check be
performed every 10 days. About 30 years ago, after solid-state
equipment became commonly available, the FAA liberalized the rule to
its present 30 day interval.

RK Henry

Most VOR receivers/heads have a fairly accessable calibration control for
the VOR and another one for the LOC. Most of us who don't choose to finance
our radio shop's owner to another week in Hawaii know how to find those
controls.

However, if you "calibrate" it, you are in violation of FAR 43. If you
"adjust" it, you are not. Go figure.

Jim



"Greg" wrote in message
oups.com...
Hi,
I recently learned that VOR can be "calibrated" or adjusted

Part of the cost of ownership, I guess. What do they charge these days
to pull out a VOR set, do a good bench check, reinstall, check the
antenna and all that stuff?

RST Engineering wrote:
Most VOR receivers/heads have a fairly accessable calibration control for
the VOR and another one for the LOC. Most of us who don't choose to finance
our radio shop's owner to another week in Hawaii know how to find those
controls.

However, if you "calibrate" it, you are in violation of FAR 43. If you
"adjust" it, you are not. Go figure.

Jim

Sam Spade wrote:
Part of the cost of ownership, I guess. What do they charge these days
to pull out a VOR set, do a good bench check, reinstall, check the
antenna and all that stuff?

Unless the error is very different at different radials there is no
need to pull the unit, the adjustment can be made on the face. Even in
high priced California they usually just ask me to put $10 in the McD's
fund for the younger techs. Total time is about 10 minutes from crawl
in to crawl out of the aircraft.

-Robert

RST Engineering wrote:
Most VOR receivers/heads have a fairly accessable calibration control for
the VOR and another one for the LOC. Most of us who don't choose to finance
our radio shop's owner to another week in Hawaii know how to find those
controls.

Easier said than done. The screw drivers that do that adjustment are
highly unique and seemingly impossible to find. My shop got theirs back
in the 50's. I spent about a month calling every place I could think of
to get the proper driver to adjust a basic King head and never got
anywhere. I think you need to wait around a shop until the old guy dies
and then grab his.

-Robert