Q: NDB Approach Tolerances
Andrew J. Wozniewicz
I have a question about NDB approaches I haven't been able to
find an authoritative answer to. The question is: how much leeway
is there in terms of a course deviation?
Here's what I mean: When flying, say, ILS, it takes full
deflection of the CDI needle to go missed. Similarly, on a VOR
approach: full deflection. How far off final approach course can
you get on an NDB approach and still consider yourself safe?
For the sake of argument, assume NDB is on the airport and is the
MAP. Specific example is NDB Rwy 16 approach to Marshfield, WI
(KMFI).
I would appreciate not so much a raw number (I've already had a
few thrown at me) as a source/regulation/rationalization, i.e.
the logic behind the number.
Thanks,
Andrew
Tom Lonsdale
Andrew J. Wozniewicz <and...@nospam.optimax.com> wrote in message
news:7p2p0i$q...@btc3.up.net...
Bob Gardner
refer to when designing approaches. In the case of an NDB the field, my
stance has always been that if you can find the NDB you have found the
airport. When the NDB is off the field, the trapezoid of protected
airspace is 2.5 miles wide at the beacon (1.25 mile either side) and
expands toward the airport, so you can be fairly well off of the
extended centerline and still be legal.
When I took my ATP checkride (with an FAA ops inspector), my NDB
approach was 9.2 miles from the beacon to the missed approach point.
This was at Paine Field, where the 747s are built, and the runway is on
the west side of the buildings. When I declared that I was at the missed
approach point and pulled off the hood, I was east of the buildings,
about 1/2 mile east of the runway. "Good approach," he said. As an
instructor and examiner, I have always assumed that a student who flies
the centerline or close to the centerline on an NDB approach with the
fix off the field is peeking.
Bob Gardner
Andrew J. Wozniewicz
> In the case of an NDB the field, my stance has always been
> that if you can find the NDB you have found the
> airport.
I am not sure I understand. I was not talking about finding the
airport; I was talking about an NDB approach, which has a
prescribed heading, ususally somewhat aligned with the runway. My
question was how far off the prescribed course a deviation is
still safe; or, IOW, how large a deviation from the approach
course necessitates going missed?
Sounds like TERPS is the ticket, but I don't have it. Can someone
shed some more light on this?
> so you can be fairly well off of the
> extended centerline and still be legal.
How far off, though?
> I have always assumed that a student who flies
> the centerline or close to the centerline on
> an NDB approach with the fix off the field
> is peeking.
Why? It surely is possible. I've done that. No peeking. <g>
Andrew
Andrew J. Wozniewicz
> If you are taking a checkride, it's 10 degrees.
No, I am not taking the checkride. I am actually flying.
Do you mind my asking where you got the 10 degrees
number? It does seem a bit restrictive for an NDB
approach.
Andrew
Chuck Forsberg
Bob Gardner <bob...@halcyon.com> wrote:
>When I took my ATP checkride (with an FAA ops inspector), my NDB
>approach was 9.2 miles from the beacon to the missed approach point.
They've apparently changed the NDB 16R approach. The MAP is 7.8
miles from the NDB. 9.2 would be the south end of the runway.
7.8 miles NDB to MAP is somewhat longer than usual.
>This was at Paine Field, where the 747s are built, and the runway is on
>the west side of the buildings. When I declared that I was at the missed
>approach point and pulled off the hood, I was east of the buildings,
>about 1/2 mile east of the runway. "Good approach," he said. As an
>instructor and examiner, I have always assumed that a student who flies
>the centerline or close to the centerline on an NDB approach with the
>fix off the field is peeking.
Or he could just be lucky that day.
During my checkride NDB approach to Salem Oregon (3.9 nm NDB to MAP)
ATC kept calling out traffic at our altitude. The DE got worried
and had me help him find the traffic. He spotted the traffic a
few seconds later, but I couldn't help but notice the runway not
quite straight ahead. Not enough time to get the hood back on, I
just hunkered down, rechecked the ADF and DF, and tweeked the course.
When the time was up I was at the MAP, 1000 feet above the threshold.
Better than some LOC/ILS approaches I've shot.....
Would I have noticed the slight course error without the peek?
Who knows. I still would have made the airport in either case.
I do check my course with the GPS track readout.
I blew an ADF approach
when the ADF quit a couple miles past the NDB because of percipitation
static. I didn't catch it as quickly as I should have.
Since then I make it a point to have the NDB obnoxiously loud when
shooting an approach with it.
I also added static wicks to N2469R and replaced some that had failed.
--
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Author of YMODEM, ZMODEM, RZ, SZ, Pro-YAM, ZCOMM, GSZ, and DSZ
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Anthony
Australia 5 degrees is the allowable tolerance although you can get away
with slightly more under certain circumstances, but certainly not on the
final decent to minimas.
Andrew J. Wozniewicz <and...@nospam.optimax.com> wrote in message
news:7p5gsn$6...@btc3.up.net...
Daniel Delaney
For an NDB approach you may not commence final decent unless you are within
5° of the final approach track i.e. if your final approach track is 160°
then you must remain between 155° and 165° (QDR or QDM as appropriate). If
you should find that you have drifted outside these limits then you must
make a missed approach and try again.
If you remember the "1 in 60 rule", if you are 10° off after 5 miles, you
are 5/6 of a mile off track and this will be 1 4/6 miles after 10 miles
personally, I find that possibility scary.
Remember the above is a limit, you should normally expect to do alot better
than that.
Incidently, you mentioned ILS and VOR, our limits state that you may not
decend on the glide slope unless the localiser is within half scale
deflection and if you go outside this, you make a missed approach. The half
scale deflection rule also applies to VOR approaches.
Again these are limits and I expect to keep the needles within 1 dot of
center unless there is a very strong gusting cross wind when I might get
away with 1.5 or 2 dots. Anything outside this and I start to think of a
missed approach.
Something to note is that the weather over here frequently requires
approaches to minima at any time of the year and Popping out of cloud on an
NDB approach bang on final approach and set up for landing is very
rewarding. Popping out of cloud and being confronted by Farmer Browns Yard
is scary.
Regards,
Danny.
Andrew J. Wozniewicz <and...@nospam.optimax.com> wrote in message
David Garrington
>As an instructor and examiner, I have always assumed that a student who flies
>the centerline or close to the centerline on an NDB approach with the
>fix off the field is peeking.
What's the point of cheating when your life may one day depend on accuracy?
I recently did some Instrument training (for UK IMC) using a local radio station mast (approx.
1000ft) as a simulated NDB approach. I was very pleased, when told to remove the foggles at 600ft to
find the mast absolutely straight ahead at about half a mile. That was NOT just a one off I'm
pleased to say. I guarantee no cheating just a lot of concentration it's much more satisfying!.
>> If you are taking a checkride, it's 10 degrees.
In the UK we have an IMC rating which allows IFR operation but not in Controlled airspace.
Requires about 15 hours instruction. I was aiming for 10 degrees or better.
>> > I have a question about NDB approaches I haven't been able to
>> > find an authoritative answer to. The question is: how much leeway
>> > is there in terms of a course deviation?
>> >
>> > Here's what I mean: When flying, say, ILS, it takes full
>> > deflection of the CDI needle to go missed. Similarly, on a VOR
>> > approach: full deflection. How far off final approach course can
>> > you get on an NDB approach and still consider yourself safe?
>> >
>> > For the sake of argument, assume NDB is on the airport and is the
>> > MAP. Specific example is NDB Rwy 16 approach to Marshfield, WI
>> > (KMFI).
>> >
>> > I would appreciate not so much a raw number (I've already had a
>> > few thrown at me) as a source/regulation/rationalization, i.e.
>> > the logic behind the number.
>> >
>> > Thanks,
>> >
>> > Andrew
>> >
>> >
>> >
Regards, David
G-BHJO, Scotland, UK
My E-mail: da...@lochaber.ftech.co.uk
Andrew J. Wozniewicz
like the concensus among the non-US pilots is between 5-10
degrees off course - go missed. In the US, no one seems to have
any clue... <g>
It is amazing that there don't seem to be clear guidelines about
it in the US... I've had raw numbers thrown at me before and am
just not happy with off-the-cuff guesses. Can anyone with TERPS
confirm what the dimensions of the protected segment for an NDB
approach are?
Thanks,
Andrew
Brett Rabe
>
> Thanks all of you who have attempted to answer my question. Seems
> like the concensus among the non-US pilots is between 5-10
> degrees off course - go missed. In the US, no one seems to have
> any clue... <g>
We never fly off-course on approaches.... :-)
Brett
--
Brett Rabe br...@uswest.net / 612.664.3078
System Guy U S WEST - Internet Services
Eagles may soar, but weasels don't get sucked into jet engines.
Dave Pullan
Andrew J. Wozniewicz <and...@nospam.optimax.com> wrote in article
<7pe692$6...@btc3.up.net>...
Can anyone with TERPS
> confirm what the dimensions of the protected segment for an NDB
> approach are?
Andrew:
In the US, for an NDB app with FAF, the primary protected area for
obstacles is 1 and 1/4 nm each side of the FAF. This distance increases
linearly to up to 2.5 nm each side when 15 nm from the FAF, unless of
course the MAP, usually the threshold, is reached.
PMurfett
In Europe it is +/- THREE degrees.
Daniel Delaney
ADF Approach +/- 5° in Europe.
Danny.
PMurfett <sni...@hotmail.com> wrote in message
news:37c14911...@news.iae.nl...
Paul Murfett
Well then, it must be a company tolerance........
Andrew J. Wozniewicz
Thanks, finally some real data.
Would you be able to tell me where/how I can get the TERPS
manual? At Sporty's they didn't even know what I was talking
about.
Andrew
Dave Pullan <dpu...@nb.sympatico.ca> wrote in message
news:01bee9de$5747fe20$Loca...@dpullan.nbnet.nb.ca...
Andrew J. Wozniewicz
I am not questioning your statement, but I was just a bit
skeptical as to the possibility of maintaining the track within
this level of accuracy.
True, The ink on my instrument rating is still a bit wet, but I
just can't imagine staying within +/- 3 deg. with a gusty
crosswind and given that my ADF is mounted on the right side, I
wouldn't even readily *see* a 3 degree deviation...
Andrew
PMurfett <sni...@hotmail.com> wrote
Don Vollum
wrote:
>
> > Here in Australia 5 degrees is the allowable tolerance
>
> In Europe it is +/- THREE degrees.
In the US ATP PTS, it states (under "TASK: NONPRECISION INSTRUMENT APPROACHES,
page 2-19), "Allows, while on the final approach segment, not more than...
+-5 degrees in the case of the RMI or bearing pointer..."
I don't have an instrument rating PTS, but it's probably got something similar.
Don
ATP/CFI
-----------------
Don A. Vollum
PelicanWare Inc
PMB 476
25 NW 23rd Pl. Ste 6
Portland OR 97210
Posted from a MessagePad 2000 with Ink Spot
andrew m. boardman
>Would you be able to tell me where/how I can get the TERPS manual?
Get it on paper from the GPO or online from:
http://afpubs.hq.af.mil/pubsforms/pubs/af/11/11022600/11022600.pdf
[Please don't quote entire articles to which you're replying.]
Matthew Whiting
>
> In message <37c14911...@news.iae.nl>, sni...@hotmail.com (PMurfett)
> wrote:
> >
> > > Here in Australia 5 degrees is the allowable tolerance
> >
> > In Europe it is +/- THREE degrees.
>
> In the US ATP PTS, it states (under "TASK: NONPRECISION INSTRUMENT APPROACHES,
> page 2-19), "Allows, while on the final approach segment, not more than...
> +-5 degrees in the case of the RMI or bearing pointer..."
>
> I don't have an instrument rating PTS, but it's probably got something similar.
My copy of the Instrument Rating PTS is 10 years old (then again,
knowing the FAA it may still be current!). It states that 10 degrees is
the bogey for both "intercepting and tracking NDB bearings" (page 1-13
of the 1989 reprint) and "NDB Instrument Approach Procedure" (page
1-16).
Holding 10 degrees really isn't hard and even 5 degrees isn't a big deal
except when the turbulence is so bad you can't read the whiskey
compass! However, you should still be able to stay within 5 degrees of
the DG, even if the DG isn't dead on.
Matt
John J. Miller
<19990826105834...@ng-fz1.aol.com>:
>>Holding 10 degrees really isn't hard and even 5 degrees isn't a big
>>deal except when the turbulence is so bad you can't read the whiskey
>>compass!
>
>
>What does this mean? If anyone knows, what is the origin of the term?
>Never ran across it before...
>
Whiskey has a very low freeze point and was used in compasses in the days
of sailing ships. Knowing this, the sailors would occasionally break the
compass to get at it - to the detriment of subsequent navigation. Other
less palatable fluids have since taken its place.
John J. Miller
jo...@mcdata.com
Roy Smith
> What does this mean? If anyone knows, what is the origin of the term? Never
> ran across it before...
Two possible explanations...
1) The fluid it's filled with is alcohol. No, it's not really, but maybe
it was at one time in history, or maybe people think it looks (or tastes?)
similar, or has been used in a pinch when the right stuff isn't available?
2) It acts like it's drunk when you turn :-)
Roy Smith
> Whiskey has a very low freeze point and was used in compasses in the days
> of sailing ships. Knowing this, the sailors would occasionally break the
> compass to get at it - to the detriment of subsequent navigation.
Was the detriment due to the effects of releasing and drinking the fluid
on the compass or on the pilot? :-)
Brett Rabe
Right. :-)
Brett
--
Brett Rabe br...@uswest.net / 612.664.3078
Insert Title Here U S WEST - Internet Services
A good compromise leaves everybody mad. -- Bill Watterson
Paul Murfett
do when the efis screen is in arc mode - so 5 degrees is 1/2inch across.
My company will fail pilots in the sim that blow +/- 3 degrees.
In article <7q11aj$a...@btc3.up.net>, and...@nospam.optimax.com says...
> Paul,
>
> I am not questioning your statement, but I was just a bit
> skeptical as to the possibility of maintaining the track within
> this level of accuracy.
>
> True, The ink on my instrument rating is still a bit wet, but I
> just can't imagine staying within +/- 3 deg. with a gusty
> crosswind and given that my ADF is mounted on the right side, I
> wouldn't even readily *see* a 3 degree deviation...
>
> Andrew
>
> PMurfett <sni...@hotmail.com> wrote
Daniel Delaney
" FINAL APPROACH SEGMENT
Precision Approach
The final approach segment begins at the Final Approach Point (FAP) - the
point on the centerline of the localiser at which the intermediate approach
altitude intersects the glide path.
Decent on the glide path shall not be initiated until the aircraft is
established within a half scale deflection of the localizer.
.......
Non Precision Approach
The final approach segment begins at the Final Approach Fix (FAF) and ends
at the Missed Approach point (MAP). The FAF should be crossed at or above
the specified altitude before descent is initiated. When no FAF is shown,
descent should not be initiated until the aircraft is established inbound
within 5° of the final approach track.
........."
The above document is the manual by which instrument procedures are
constructed. Note the limits laid down. If your company has higher operating
requirements then I commend them but they are a requirement for your company
alone.
The above information is also as far as I know repeated in the Jeppesen
Airway Manual under "Air Traffic Control" and in the Aerad Manual "Flight
Information Supplement".
Regards,
Danny.
Paul Murfett <sni...@hotmail.com> wrote in message
news:MPG.1233d8def...@news.iae.nl...