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.