Timing a localizer approach

[acat]

Hi,
I was wondering what others opinions are on this. If you are shooting a localizer approach and you have an IFR GPS and the approach is timed is it necessary to time it for the missed? The GPS tells you when you are at the missed and is a lot more accurate then time in my opinion. It is a ground based approach though so I think technically you shouldn't use a GPS except for situational awareness. Even if I did time them all I would trust the gps 100 times more than a clock to tell me when to go missed. I usually set the timer just because I was taught that way but what are your procedures.

Thanks

 

[minitour]

That's fantastic.........until the GPS loses RAIM or fails altogether.

-mini

 

[midlifeflyer]

I think that hitting the timer is somewhat equivalent to using your car's turn signal at 3 am on a deserted road. Probably not necessary but if it's developed as an automatic habit, it's one less thing to think about and you're less likely to forget it when you do need it.

Besides, so much about flying is based on redundancy and cross=referencing for safety.

 

[SiuDude]

That's fantastic.........until the GPS loses RAIM or fails altogether.

-mini

If that happens, go missed, re-brief, and try it again.

 

[CaptETWes]

If that happens, go missed, re-brief, and try it again.

What if you're flying paying passengers or the "boss?" What if you were trying the approach in icing conditions? There are so many reasons why you should just time and hopefully complete the approach.

I see nothing wrong with using the GPS, but I would still time. WHY? Because if you were to get a RAIM failure message, you would just look at your time and complete the approach. Taking that two seconds it requires to start a watch or on-board clock can save lots of time, money, and stress. Besides, I would look to find where it says GPS can substitute for required timing on a localizer approach. To the FAA, even IFR GPS is considered a situational awareness tool. The AIM says there is a list of items that GPS can be used to substitute for. I don't remember of the top of my head that timing on an approach was one of them. I think that if you were to bust a reg and said you were using GPS to find your missed approach point (where timing is involved), they would come down on you hard. Just my two cents. Please, if you find anything that disputes what I've said, let me know. Cheers.

 

[minitour]

If that happens, go missed, re-brief, and try it again.

How do you know where the MAP is if you didn't start time and your GPS took a crap?

I'd agree with you on what to do, but I'm a little fuzzy on how to do it if you lost a piece of nav equipment.

-mini

 

[satpak77]

Not a good idea...

Hi,
I was wondering what others opinions are on this. If you are shooting a localizer approach and you have an IFR GPS and the approach is timed is it necessary to time it for the missed? The GPS tells you when you are at the missed and is a lot more accurate then time in my opinion. It is a ground based approach though so I think technically you shouldn't use a GPS except for situational awareness. Even if I did time them all I would trust the gps 100 times more than a clock to tell me when to go missed. I usually set the timer just because I was taught that way but what are your procedures.

Thanks

I struggled to find a "pure LOC" approach, found alot of LOC/DME or "ILS or LOC/DME" and found this one at KSAN

http://myairplane.com/databases/approach/pdfs/00373L27.PDF

Notice the MAP is based on time, and DME is NOT required on this approach, or it would be called "LOC/DME"

With that said, the FAA went ahead and displayed the MAP as 1.3 DME off the LOC signal. You can see the MAP physically appears as the Runway 27 threshold basically. So how is GPS going to define the MAP on this approach?

With that said, GPS could assist your S/A by showing you if yes/no you flew past the airport already, ala Hendricks Racing King Air crash.

BUT: The GPS will use the airport lat/long, which could be the center of the field, which may be far off from the MAP point. Imagine the center of DFW, versus the runway threshold of one of the runways. We are talking maybe 2 miles away. BUT, GPS could be a "advisory" tool.

REEBO, the FAF, is defined as 6.4 DME off the LOC (but remember, DME is not required) OR the 304 radial off Poggi. That is when you start your time, theoretically when the LOC and VOR radial perfectly intersect. As a back-up, you could put REEBO in the GPS, if IFR approved, and then monitor how many miles you have flown. It is 5.1 until the MAP. This however can be a little tricky.

GPS is a fine "heads up" tool, but if its not a "GPS Approach", then it is advisory only, not primary. By the way, if you have it, USE IT. Plug in the airport and at least in the soup, hard IFR, ice pellets on your non-heated windshield, you have a back-up for that timer or DME. USE ALL AVAILABLE information as long as it does not cause confusion or overload.

Lets take a look at the Hendricks report, page 17 of the pdf file, under "Analysis", second paragraph

http://www.ntsb.gov/Publictn/2006/AAB0601.pdf

Basically, at the MAP (physically basically the Runway 30 threshold), they should have flown to BALES and held. BALES is the NDB beacon.

They were flying the LOC 30 approach

http://myairplane.com/databases/approach/pdfs/05648L30.PDF

They crashed when they flew 8 miles PAST the airport and then began attempted missed approach procedures.

It has been discussed that they had an out-of-date GPS receiver, and a few guys stated it was physically mounted in a hard-to-see place. However, simply by punching in "KMTV" airport and monitoring the DME to the field, even if the GPS was out of date (did they move the airport?), possibly would have saved these guys from getting killed.

Note: The accident airplane had no FDR. Interviews with Hendricks pilots claimed that the dead pilots had all used the GPS before and used BALES and the VOR as waypoints. (Author's note: raised eyebrows on this one)

FYI

 

[SiuDude]

How do you know where the MAP is if you didn't start time and your GPS took a crap?

I'd agree with you on what to do, but I'm a little fuzzy on how to do it if you lost a piece of nav equipment.

-mini

What I was getting at is that a complete GPS failure, without any of the other avionics failing, is highly unlikely. Even with a RAIM message, your position should be fairly accurate, albeit not within standards. While timing a LOC approach is not as ridiculous as timing an ILS, I am still going to stick with my answer.

Regards,
Devil's advocate

 

[minitour]

What I was getting at is that a complete GPS failure, without any of the other avionics failing, is highly unlikely. Even with a RAIM message, your position should be fairly accurate, albeit not within standards. While timing a LOC approach is not as ridiculous as timing an ILS, I am still going to stick with my answer.

Regards,
Devil's advocate

I see where you're coming from, I've always tended to look at IFR procedures as "oh crap...everything is going to fail..." scenarios. That way the one time everything does fail, I've got a sporting chance. Two different schools of thought I guess...neither one really wrong...just different.

-mini

 

[A Squared]

With that said, the FAA went ahead and displayed the MAP as 1.3 DME off the LOC signal. You can see the MAP physically appears as the Runway 27 threshold basically. So how is GPS going to define the MAP on this approach?.................. BUT: The GPS will use the airport lat/long, which could be the center of the field, which may be far off from the MAP point. Imagine the center of DFW, versus the runway threshold of one of the runways. We are talking maybe 2 miles away.

Many IFR GPS units will give you the same distance as the ILS DME if you enter IUBR

works good, lasts long time.

 

[FL420]

Many IFR GPS units will give you the same distance as the ILS DME if you enter IUBR

works good, lasts long time.

Yes. But if a localizer does not have a co-located DME, the location of the LOC antenna(Lat/Long) may or may not be surveyed and in the database. I read somewhere recently(sorry, I can't provide a reference at present) that the FAA is working on the problem so eventually GPS users can use the GPS distance for determining the MAP.

 

[minitour]

Yes. But if a localizer does not have a co-located DME, the location of the LOC antenna(Lat/Long) may or may not be surveyed and in the database. I read somewhere recently(sorry, I can't provide a reference at present) that the FAA is working on the problem so eventually GPS users can use the GPS distance for determining the MAP.

Fantastic! The next thing they need to work on is letting us w/o an ADF shoot an NDB approach w/o a GPS overlay provided the procedure is in the database.

-mini

 

[A Squared]

Fantastic! The next thing they need to work on is letting us w/o an ADF shoot an NDB approach w/o a GPS overlay provided the procedure is in the database.

-mini

Hmmm, I'm a little unsure what you're saying here, if the NDB procedure is in the GPS database, it *is* an overlay. If there's an overlay, you can shoot the approach using a GPS (assuming approach approved receiver)

 

[Flysher]

Hmmm, I'm a little unsure what you're saying here, if the NDB procedure is in the GPS database, it *is* an overlay. If there's an overlay, you can shoot the approach using a GPS (assuming approach approved receiver)

I think he meant if you dont have an ADF in the cockpit. If I recall correctly you CANT use the GPS in that case. This is without the FAR/AIM in front of me, but I also think that if you have a WAAS GPS you ARE allowed to use it for an NDB approach, someone correct me if Im wrong though.

 

[minitour]

Hmmm, I'm a little unsure what you're saying here, if the NDB procedure is in the GPS database, it *is* an overlay. If there's an overlay, you can shoot the approach using a GPS (assuming approach approved receiver)

I've seen approaches in the GPS for the "NDB XX" approach and the airport only has one approach plate...it's the "NDB XX" approach.

If I don't have an ADF, I can't shoot the approach...even though the GPS is much more accurate.

Flysher,
I wasn't aware of the WAAS GPS for NDB approaches w/o an ADF thing...I'll check it out.

-mini

 

[Flysher]

yea like i said my FAR/AIM isnt with me right now so i cant check, but i think i remember reading that. I know that with a WAAS GPS you dont have to have any other kind of "supplemental" navigation like you do right now with GPS, you can just have your GPS unit and thats it.

 

[nosehair]

"Timing" is not a 'regulatory' requirement on any non-precision approach. It is a long standing teqhnique by which we make an estimate of our position on the approach. We 'wag' and guess at the effects of the head or tail wind, but as we all know, it is a guess - without DME or other ground measuring equipment.

If you study the characteristics of a localizer needle as you approach the end of the runway, you can make a much more accurate 'wag' at reaching the runway than with timing. If you've ever had an unobserved strong headwind on a localizer approach, you have probably observed that the 'estimated time' ran out a mile or two from the runway, and the localizer needle had not yet become so sensitive. Learn to correlate the needle movement with Middle Marker passage or runway environment and you will know better when to start a missed. It will also prevent an overshoot when you have a strong tailwind.

Always time because that gets you in the ballpark and 'times' your more accurate estimation by the movement of the needle or other means such as a GPS.

This is not saying to make your decision solely on GPS, or needle movement or time, you should take all factors into account.

 

[A Squared]

I think he meant if you dont have an ADF in the cockpit. If I recall correctly you CANT use the GPS in that case. This is without the FAR/AIM in front of me, but I also think that if you have a WAAS GPS you ARE allowed to use it for an NDB approach, someone correct me if Im wrong though.

Ok, I wasn't commenting on the "without a ADF" part of his statement, I was commenting on the second part of statement, the part where he seems to me to be referring to NDB approaches where "the procedure is in the database" but there is no overlay. My point was this: If the NDB approach is in the GPS database (not just the NDB position) that *IS* an overlay, there's no such thing as an approach that is in the database, but there is no overlay. That's what an overlay *is* a procedure based on another navaid which is in the GPS database as a selectable approach procedure.

Now, to take it one step further, whether or not you can fly the approach without an NDB installed depends on the Phase of the approach. (phase of the overlay program) There are no more Phase I approach overlays. If it's a Phase II overlay, the title will say NDB RWYXXX with no mention of GPS and you have to have an ADF installed, If it's a Phase III overlay, the title on the plate will say NDB or GPS RWY XXX, you can fly the approach with no ADF installed.

I don't know how many Phase III approaches there are left, I can't think of any off the top of my head. In my area they seem to have all been replaced with RNAV only procedures. Your results may vary I do know of a few Phase II approaches that are still lurking in the databases

 

[Flysher]

ah ok, sorry about that

 

[MauleSkinner]

As Nosehair said, timing is how we estimate our position relative to estimates of headwind/tailwind component, etc.

Personally, I think that the thought process in timing an approach is important. You have to think about the winds, your airspeed, and how they affect your groundspeed, and while you're thinking about it, your track and wind correction angle become part of the conscious process as well. In other words, it forces you to think about what's going on around you, and you get a bigger picture of what you're doing. The big picture, IMO, is almost always good.

Figuring out the time required forces you to estimate a groundspeed on the approach. If you don't have a groundspeed in mind, you might not notice that the front went through recently, and you're now shooting the approach with a 20-knot tailwind. Yes, in this case your time estimate would be way off. That's why you DO look at your GPS to compare groundspeeds and distance to the MAP, and take appropriate action to either go missed in the "right place", or find out whether or not the surface winds are what you thought they were so that you can take appropriate action (straight-in or circle).

If timing the approach is all you've got, then timing the approach is all you've got. If GPS is all you've got, then GPS is all you've got. But don't throw good tools out of the cockpit simply because they're not as accurate as you might think necessary or desirable.

Fly safe!

David