GPS backup

[Pinecone]

DME limit is about 100 aircraft per transmitter. 252 frequencies for DME.

Stations are not huge, would not be hard to place them at other (cell, repeater, etc) transmitter sites.

And DME/DME navigation has been around for a long time. So not inventing anything new.

 

[denverpilot]

DME limit is about 100 aircraft per transmitter. 252 frequencies for DME.

Stations are not huge, would not be hard to place them at other (cell, repeater, etc) transmitter sites.

And DME/DME navigation has been around for a long time. So not inventing anything new.

Yeah I didn’t want to look up the limits but was responding to those who said “just add DME/DME RNAV to everything”… as a backup to GPS”.

That’ll overload the available DME ground stations quick in some areas. Not really viable. I knew there was a fairly low limit — just by the fact that it’s a transponder based system.

Thanks.

 

[Bob Noel]

typically, it's viewed as about 100 aircraft...

a bit of trivia, consider that overlapping interrogations aren't as much of a problem as you'd think. Imagine a DME ground station receiving the interrogation pulse pairs from two aircraft at exactly the same time. So what... It'll just look like a stronger (probably somewhat misshapen) interrogation and transmit one reply pulse pair... both aircraft will get to use that one pulse pair. And they have to be able to handle overlapping interrogations (the first pulse of a second interrogation arriving before the second pulse of the prior interrogation).

I vaguely remember the specification for the DME/P portion of MMLS had to be able to transmits upto 4000 pulses (pulses, not pulse pairs)... but that DME/P was only intended to support terminal area operations.

How many aircraft are within line of sight of high density places like Chicago or LAX?

 

[Pinecone]

Yeah I didn’t want to look up the limits but was responding to those who said “just add DME/DME RNAV to everything”… as a backup to GPS”.

That’ll overload the available DME ground stations quick in some areas. Not really viable. I knew there was a fairly low limit — just by the fact that it’s a transponder based system.

Thanks.

A hundred planes in the service volume of a single DME station is a LOT of planes.

And a DME/DME nav system would be using closer DMEs versus ones far away. O'Hare has about 78 operations per hour on average.

 

[AV8R_87]

Last time I bothered looking at the sensors page in the FMS, it was tracking DMEs 50-100nm away. Use an average of 75nm and that's 18 thousand square nautical miles that could be covered by one DME.
That would be a plane for 180 square nm, or a square 13nm on each side. I could see some busy areas having their DMEs overwhelmed.

 

[Pinecone]

The question would also be, how often does a DME/DME have to ping the DME versus the rate the DME does so?

Especially for GA, we don't move that fast that we need an update every second or two.

 

[AV8R_87]

You need a minimum number of pulses and replies to ensure the DME is replying to you and not someone else.
During the initial search phase, the interrogator sends 150 pulse pairs per second, dropping to 30 PPS for the tracking phase.
A DME usually transmits 2700 PPS, regardless of the number of aircraft interrogating it. It will continuously adjust the receiver gain to achieve that pulse rate. In a low traffic environment, that mesns it will reply to random receiver noise, while in a high traffic environment that will cause it to ignore the more distant (weaker) interrogations.

 

[Bob Noel]

The MMLS DME/P will transmit a minimum of 1000 pulses per second (referred to as squitter pulses).

Actually, I don’t know if there are any operational MMLS units are out there anymore

 

[flyingtexas]

My paper map, watch and ruler, and a compass.
Being able to do basic math and some trig doesn't hurt, either.
I wish planes still had ADF.
Not without it's issues, but I flew a lot of miles, AM radio station to AM radio station, back in the day.

i really wish they still had a class somewhere to teach it. problem is, just about every airplane is going to need a new dashboard to install the receivers. still, i would like to actually use and NDB just to see what it's like

 

[RussR]

i really wish they still had a class somewhere to teach it. problem is, just about every airplane is going to need a new dashboard to install the receivers. still, i would like to actually use and NDB just to see what it's like

If you're flying a glass panel airplane, many of them can give you half the experience of an NDB by using the bearing pointer function. It will just point directly at whatever you tell it to, just like an ADF. You could fly some mock approaches like this if you wanted. Of course, you won't get the experience of continually monitoring the ID, nor will the needle oscillate back and forth like a real one.

 

[midlifeflyer]

If you're flying a glass panel airplane, many of them can give you half the experience of an NDB by using the bearing pointer function. It will just point directly at whatever you tell it to, just like an ADF. You could fly some mock approaches like this if you wanted. Of course, you won't get the experience of continually monitoring the ID, nor will the needle oscillate back and forth like a real one.

All true.

The funny thing is, though, I hated ADF but love bearing pointers.

We have one of the 175 or so NDB approaches left in the US near me. I keep waiting for someone with an ADF to ask for an IPC

 

[asicer]

We have one of the 175 or so NDB approaches left in the US near me. I keep waiting for someone with an ADF to ask for an IPC

I count 138:

79J KMGM KTOI KRUE KRYN KRQE KINW KSIY KITR KCOS KHST X51 KHEG 07FA KTMB KMIA KFFC KBHC 70J KFZG KMLJ KOPN KTVI KHQU KWDR KSUN KALN KBLV KCPS KMDH KFWC KOLY KPIA KUIN 2H0 KCFJ KJVY KUWL KGBD KHRU KHUT KOIN KSYF KSLN KICT KBWG KDVK KHOP KLOU KBQP KDRI KIER KCQX KPVC KNHK KONZ KGOV KPHN KCIU KIRS KFOZ KRYM KLJF KLXL KSTL KSUS KHSA KTUP KVUJ KECG KHRJ KAKH KRUQ KEHO KCPC KCDR KCNP KFBY KFMZ KGRN KGGF KODX KOKS KPMV KVTN KAHQ KJYR KCNH KDAW KNEL KIAG KSCH KAKR KUNI KTZR KOSU KMGY 1G3 KMFD 16G I23 KYNG KGUY KLGD KHIO KMUI KAIK KDCM KMNI KEOE KDYB KEOD KSRB KATA KHYI F17 23R KHLR KCXO KPYX KSJT KSNK KCNW KBKT KCJR KDAA KEZF KLUA KSHD KAKQ KAWO KFHR KMWH KOSH KCMY KRYV KGUR KTOR

 

[flyingcheesehead]

I count 138:

79J KMGM KTOI KRUE KRYN KRQE KINW KSIY KITR KCOS KHST X51 KHEG 07FA KTMB KMIA KFFC KBHC 70J KFZG KMLJ KOPN KTVI KHQU KWDR KSUN KALN KBLV KCPS KMDH KFWC KOLY KPIA KUIN 2H0 KCFJ KJVY KUWL KGBD KHRU KHUT KOIN KSYF KSLN KICT KBWG KDVK KHOP KLOU KBQP KDRI KIER KCQX KPVC KNHK KONZ KGOV KPHN KCIU KIRS KFOZ KRYM KLJF KLXL KSTL KSUS KHSA KTUP KVUJ KECG KHRJ KAKH KRUQ KEHO KCPC KCDR KCNP KFBY KFMZ KGRN KGGF KODX KOKS KPMV KVTN KAHQ KJYR KCNH KDAW KNEL KIAG KSCH KAKR KUNI KTZR KOSU KMGY 1G3 KMFD 16G I23 KYNG KGUY KLGD KHIO KMUI KAIK KDCM KMNI KEOE KDYB KEOD KSRB KATA KHYI F17 23R KHLR KCXO KPYX KSJT KSNK KCNW KBKT KCJR KDAA KEZF KLUA KSHD KAKQ KAWO KFHR KMWH KOSH KCMY KRYV KGUR KTOR

Do any of those airports have more than one NDB approach?

They're going away quickly. And despite being well trained on NDBs, and having about the best setup possible for flying an NDB approach (electronic RMI function on the Argus 7000) for the first six years I had the airplane I never flew one, even for practice. There's pretty much always a better option these days.

Are any of these still overlay approaches? ("NDB OR GPS") Are there any VOR overlays remaining?

 

[midlifeflyer]

I count 138:

79J KMGM KTOI KRUE KRYN KRQE KINW KSIY KITR KCOS KHST X51 KHEG 07FA KTMB KMIA KFFC KBHC 70J KFZG KMLJ KOPN KTVI KHQU KWDR KSUN KALN KBLV KCPS KMDH KFWC KOLY KPIA KUIN 2H0 KCFJ KJVY KUWL KGBD KHRU KHUT KOIN KSYF KSLN KICT KBWG KDVK KHOP KLOU KBQP KDRI KIER KCQX KPVC KNHK KONZ KGOV KPHN KCIU KIRS KFOZ KRYM KLJF KLXL KSTL KSUS KHSA KTUP KVUJ KECG KHRJ KAKH KRUQ KEHO KCPC KCDR KCNP KFBY KFMZ KGRN KGGF KODX KOKS KPMV KVTN KAHQ KJYR KCNH KDAW KNEL KIAG KSCH KAKR KUNI KTZR KOSU KMGY 1G3 KMFD 16G I23 KYNG KGUY KLGD KHIO KMUI KAIK KDCM KMNI KEOE KDYB KEOD KSRB KATA KHYI F17 23R KHLR KCXO KPYX KSJT KSNK KCNW KBKT KCJR KDAA KEZF KLUA KSHD KAKQ KAWO KFHR KMWH KOSH KCMY KRYV KGUR KTOR

I didn't count them. I just put NDB in the advanced search box at the IFL gateway and it came up with 179 with "NDB" somewhere in the title. I knew that some of them would be combinations like "ILS OR LOC NDB" or "COPTER" specific, so I knocked off a few and came up with a average. I wasn't treating multiple NDB approaches to the same airport as one. Hence, "or so."

 

[asicer]

My bad, it's actually 124:

79J KMGM KTOI KRUE KRYN KSIY KITR KCOS KHEG KFFC KBHC 70J KFZG KMLJ KOPN KTVI KHQU KWDR KSUN KMDH KFWC KOLY KPIA KUIN 2H0 KCFJ KJVY KUWL KGBD KHRU KHUT KOIN KSYF KSLN KICT KBWG KDVK KHOP KLOU KBQP KDRI KIER KCQX KPVC KNHK KONZ KGOV KPHN KCIU KIRS KFOZ KRYM KHSA KTUP KVUJ KECG KHRJ KAKH KRUQ KEHO KCPC KCDR KCNP KFBY KFMZ KGRN KGGF KODX KOKS KPMV KVTN KAHQ KJYR KCNH KDAW KNEL KIAG KSCH KAKR KUNI KTZR KOSU KMGY 1G3 KMFD 16G I23 KYNG KGUY KLGD KHIO KMUI KAIK KDCM KMNI KEOE KDYB KEOD KSRB KATA KHYI F17 23R KHLR KCXO KPYX KSJT KSNK KCNW KBKT KCJR KDAA KEZF KLUA KSHD KAKQ KAWO KFHR KMWH KOSH KCMY KRYV KGUR KTOR

I forgot to filter out things like "SNDBR THREE" and "LINDBERGH EIGHT".

Do any of those airports have more than one NDB approach?

79J, KHRU, KIRS KFMZ, KPMV, KJYR, KRYV, KTOR

Are any of these still overlay approaches? ("NDB OR GPS")

KSIY, KCNP

Are there any VOR overlays remaining?

Not sure what to look for here.