VOR approach- when to descend from the FAF

When flying a VOR approach in which the FAF is defined by the VOR, is
it appropriate to start the descent to the MAP, or next stepdown,
immediately after overflying the VOR or should I wait until I have
positive course guidance for the final approach segment?

I ask because it can sometimes take 1-2nm for the CDI to move, which
may require a rushed descent to the MAP on some approaches.

Les Ismore wrote:

<<Well, that is precisely the reason why it is bad advice to start
down
with no indication of movement of the needle. >>

I think your advice is good and would be more easily defensible if you
were being evaluated by a check airman. Very few of them are TERPS
experts.

Les Izmore wrote:

<<This is being treated like some kind of academic angels-on-the-head-
of-a-pin question. It is not. >>

Not to you, maybe. People ask questions here for a variety of
reasons: 1) legality, 2) safety, 3) passing checkrides, 4) curiosity,
etc.

Regarding safety, no doubt you're 100% correct.

We have a local VOR approach with a course change at the FAF and a
high descent gradient on final. Without descending immediately pass
the VOR, the odds of getting in shrink rapidly.

Peter wrote:
<<For what this is worth, on the European IR one is not supposed to
descend (from the platform altitude) unless one is established within
5 degrees of the track. I don't know the reference but this is what I
was always taught. To me, it makes sense and the only time I would
deviate from it would be
>>

ICAO standards for "established" are 1/2 scale deflection. The US
doesn't have a similar definition, unfortunately. Sam Spade was
arguing that, over the VOR, that standard doesn't have much meaning.
For a staying-in-protected-airspace point of view, I'm sure he's
correct.

Greg Esres wrote:
> Peter wrote:
> <<For what this is worth, on the European IR one is not supposed to
> descend (from the platform altitude) unless one is established within
> 5 degrees of the track. I don't know the reference but this is what I
> was always taught. To me, it makes sense and the only time I would
> deviate from it would be
>
>
> ICAO standards for "established" are 1/2 scale deflection. The US
> doesn't have a similar definition, unfortunately. Sam Spade was
> arguing that, over the VOR, that standard doesn't have much meaning.
> For a staying-in-protected-airspace point of view, I'm sure he's
> correct.

Correct. The protected airspace for a VOR IAP overhead the VOR when
it's the FAF is 1 mile each side of the station. This width expands as
the aircraft departs the VOR/FAF. The maximum course change permitted
at the VOR/FAF is 30 degrees.

Descent shouldn't be made unless the pilot is tracking on course inbound
to the VOR/FAF. If he is on course as station passage occurs, and a
course change is required, a turn to intercept while commencing descent
is expected in the design of the criteria; i.e., the descent gradient is
calculated from the VOR/FAF, not from some imaginary post-facility point
of intercept, and the maneuver required to reintercept is minimal
assumming reasonable comptetency.

Greg Esres wrote:

> Les Izmore wrote:
>
> <<This is being treated like some kind of academic angels-on-the-head-
> of-a-pin question. It is not. >>
>
> Not to you, maybe. People ask questions here for a variety of
> reasons: 1) legality, 2) safety, 3) passing checkrides, 4) curiosity,
> etc.
>
> Regarding safety, no doubt you're 100% correct.
>
> We have a local VOR approach with a course change at the FAF and a
> high descent gradient on final. Without descending immediately pass
> the VOR, the odds of getting in shrink rapidly.

Not to mention real issues trying to do a slam-dunk low to the ground.

On 02/21/08 09:27, gatt wrote:
> "Terence Wilson" <tez@latte.com> wrote in message
> news:0a8fr318sgt2tei07a5ede7f1r3gbgjsmt@********...
>> When flying a VOR approach in which the FAF is defined by the VOR, is
>> it appropriate to start the descent to the MAP, or next stepdown,
>> immediately after overflying the VOR or should I wait until I have
>> positive course guidance for the final approach segment?
>>
>> I ask because it can sometimes take 1-2nm for the CDI to move, which
>> may require a rushed descent to the MAP on some approaches.
>
> I spend that minute or so making sure my heading and approach airspeed are
> under control, and then simply catch up to the descent afterward when the
> needle comes back. It'll be interesting to see how other people do it, but
> that's the way I was trained.
>
> -c
>
>

I was taught to begin the descent at station passage (using the 5 'T's).
It's never taken more than just a very few seconds for the CDI to start
coming back in. A minute seems awfully long.

By the way, if the needle doesn't come back in, I would go missed. The
first thing I do there is begin a climb. I really don't see how it causes
any problems to begin the descent at station passage (assuming that is
what the procedure calls for, of course).


--
Mark Hansen, PP-ASEL, Instrument Airplane, USUA Ultralight Pilot
Cal Aggie Flying Farmers
Sacramento, CA