wardialer
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ILS With Same NAV Freq.? Almost Made Me Crash

Wed Jan 06, 2010 5:52 pm

Hi,

If your a pilot, can you tell me on how you deal with this scenario?

Ok, lets take KLAX (Los Angeles Airport) which for runways 25L/7R they have the same ILS Frequency as 109.90. Also for runways 24R/06L which for BOTH of them has ILS frequency of 108.50.

Now, on Flight Simulator when I was doing a stright-in ILS approach for runway 25L using 109.90, all of a sudden it grabbed the ILS but the aircraft just flew crazy and erratically.

Now, I have done some investigating as shown below which MAY have cause this error.

Runway 25L has an IDENT of ILAX, and runway 7R has the IDENT of IMKZ but SAME ILS frequency. After this investigation, I setup my ILS approach again for 25L, and I noticed before on the Map Nav Page, that it had the IDENT as IMKZ (ILS ID CODE for 7R) around 30 NM out from KLAX. But then when I got closer to the approach path, it did change over to ILAX (ILS ID CODE for 25L)

So my question is, how far out can you enable the NAV/APP switch in order to prevent this "mix-up" which almost made me crash during the approach....????

I looked over the charts, but never thought using a different IDENT CODE with the same ILS Freq would cause my aircraft to behave erratically.

Does this happen in real flight???

If your a captain or a co-pilot, then please respond or anyone who is familiar with this sort of misconception.

Thx.

[Edited 2010-01-06 09:54:56 by wardialer]

[Edited 2010-01-06 09:57:10 by wardialer]
 
Goldenshield
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RE: ILS With Same NAV Freq.? Almost Made Me Crash

Wed Jan 06, 2010 6:16 pm



Quoting Wardialer (Thread starter):
So my question is, how far out can you enable the NAV/APP switch in order to prevent this "mix-up" which almost made me crash during the approach....????

In real life, they will only have the localizers for the runway in use on, i.e.; landing 25L, they will turn on the 25L localizer, and turn off the 7R localizer---especially since they share the same frequency.
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Mir
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RE: ILS With Same NAV Freq.? Almost Made Me Crash

Wed Jan 06, 2010 6:50 pm



Quoting Wardialer (Thread starter):
Does this happen in real flight???

Sure. Unlike in Flight Simulator, however, the ILS systems for both runways will not be on at the same time - they only turn on ILS for the one that they're using. It makes sense to do this, since you're not going to be using both of them at the same time anyway, and it allows you to use one frequency for two runways, which leaves more frequencies available for all the other runways in the area.

The thing to do in real flying is to check the identifier of the localizer - if it doesn't match the one on your approach chart, don't shoot the approach. In FS, it probably means that you're closer to the wrong end of the runway than you are to the correct one (happens most often on a downwind before you're abeam midfield). In real life, it means that they didn't switch the localizers, and you should contact ATC and tell them to do so.

Happened to me once - was approaching HPN and they had just switched from using 16 to 34. Conditions were VMC, and they were using visual approaches, but we wanted to shoot the ILS for training purposes. Turned the localizer, checked the identifier, and it didn't match. First thought - is that the test signal? Second thought - check the 16 chart (which, in retrospect, probably should have been the first thought - file that for future use). Sure enough, it was the identifier for the 16 ILS. Called ATC and let them know about it. After two or three times telling them that yes, we were sure, the identifier went offline for a couple of seconds, and then the correct one started beeping.

The reason FS does what it does is that it's a sim, and if people want to shoot an ILS to a runway with a 30 knot tailwind just to show that they can, why not? So they use a solution that, while not entirely realistic, suffices for what they need it to do.

-Mir
7 billion, one nation, imagination...it's a beautiful day
 
wardialer
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RE: ILS With Same NAV Freq.? Almost Made Me Crash

Wed Jan 06, 2010 7:19 pm

Ahhhhhh...So in "real-flying" they turn one ILS operational runway on or off. Ok, that makes sense.

Of course, FSX flight simulator is NOT 100% realistic, but never came accross this issue.
Good to know.

So in real flights, when ever this happens and we all know it wont or never has....can this even happen if BOTH ILS CODES or FREQS are enable for that particular runway so the aircraft would just loose control and fall out of the ILS Glideslope????

And of course, real pilots have to tune into the latest ATIS information as well to find out which ILS runways are in use.

Nextime, I will keep a very close eye on the MAP NAV DISPLAY esp. on the upper right-hand corner next to the ILS course the IDENT CODE. That solved the issue.....So when it changes from IMKZ to ILAX thats when the NAV/APP should be enabled in Flight Sim. But as you said, for real flying, you dont need to because the ILS CODE or freq for that runway would be enabled and other one disabled....And ATIS is helpful too...

Thx.
 
KELPkid
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RE: ILS With Same NAV Freq.? Almost Made Me Crash

Wed Jan 06, 2010 7:24 pm



Quoting Mir (Reply 2):
The thing to do in real flying is to check the identifier of the localizer - if it doesn't match the one on your approach chart, don't shoot the approach.

Do the avionics in a glass cockpit typically take care of this for you over in part 121 land? I know that identifying navaids (by pulling the little IDENT knobs on the radio stack) is required for GA IFR....I have seen a few cockpit videos of approaches, and it doesn't seem that modern airline aircrews worry too much about the 5 T's and identifying navaids  Wink
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DiamondFlyer
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RE: ILS With Same NAV Freq.? Almost Made Me Crash

Wed Jan 06, 2010 7:47 pm



Quoting KELPkid (Reply 4):
Do the avionics in a glass cockpit typically take care of this for you over in part 121 land? I know that identifying navaids (by pulling the little IDENT knobs on the radio stack) is required for GA IFR....I have seen a few cockpit videos of approaches, and it doesn't seem that modern airline aircrews worry too much about the 5 T's and identifying navaids

I can't answer the 121 questions, but even in the GA environment, there is equipment that auto-identifies. The Garmin GNS530 does it, as does their G1000 system. Really makes it almost to easy to do IFR flying today.

-DiamondFlyer
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Mir
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RE: ILS With Same NAV Freq.? Almost Made Me Crash

Wed Jan 06, 2010 8:09 pm



Quoting KELPkid (Reply 4):
I know that identifying navaids (by pulling the little IDENT knobs on the radio stack) is required for GA IFR....

Hell, the G1000 will show you the ID. I tend to check it myself with the audio, but I'll admit to forgetting sometimes.

Quoting KELPkid (Reply 4):
it doesn't seem that modern airline aircrews worry too much about the 5 T's and identifying navaids  

I flew in the sim with a guy (former 747 captain for a major EU carrier) who was pretty good about basic instrument flight (example: I was dealing with an emergency checklist and getting set up for the approach, and since I needed some more time, we asked for, and got, a hold). I was all set to program the hold into the FMC (which doesn't always work the first time around), but he just waved me off and told me to worry about the checklist and that he'd just fly the hold manually (well, on autopilot with the heading bug, the CDI, and the clock). And once I finished with the checklist and did manage to get the hold put in, he was pretty much spot on. We didn't bother identifying navaids though (except for NDBs).

Quoting Wardialer (Reply 3):
So when it changes from IMKZ to ILAX thats when the NAV/APP should be enabled in Flight Sim.

I wouldn't be engaging APP until you've been given the intercept to final and cleared for the approach (with the correct identifier showing).

Quoting Wardialer (Reply 3):
But as you said, for real flying, you dont need to because the ILS CODE or freq for that runway would be enabled and other one disabled...

Well, you want to make sure that the code is correct. That's one of the ways of ensuring that you have the right frequency tuned in (I have seen someone try to intercept a localizer while having a completely different localizer tuned - needless to say, it didn't work too well).

-Mir
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swiftski
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RE: ILS With Same NAV Freq.? Almost Made Me Crash

Wed Jan 06, 2010 8:33 pm



Quoting Wardialer (Thread starter):
ILS With Same NAV Freq.? Almost Made Me Crash

Gees I thought you were an airline pilot that just nearly lost a 747 with that headline.
 
Fabo
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RE: ILS With Same NAV Freq.? Almost Made Me Crash

Wed Jan 06, 2010 10:37 pm

It is fine in FS. You just need to make sure you dont push the APP button until you are on correct side. In fact, I wonder, if that could work in real life - localizer, if it can transmit both ways, is obviously not a concern, and I guess glideslopes would not interfere, as they point opposite ways?
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N353SK
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RE: ILS With Same NAV Freq.? Almost Made Me Crash

Wed Jan 06, 2010 10:44 pm



Quoting Fabo (Reply 8):
I guess glideslopes would not interfere, as they point opposite ways?

The localizer signal is bi-directional. A Localizer Backcourse approach uses the backside of the localizer signal.
 
IAHFLYR
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RE: ILS With Same NAV Freq.? Almost Made Me Crash

Thu Jan 07, 2010 4:46 am



Quoting Swiftski (Reply 7):
Gees I thought you were an airline pilot that just nearly lost a 747 with that headline.

Me too, I'm thinking wonder where this happened!

Quoting N353sk (Reply 9):
The localizer signal is bi-directional. A Localizer Backcourse approach uses the backside of the localizer signal.

Not always. There are numerous runways with a glideslope antenna on both ends of the runway, in which case a localizer interlock is used when localizer is switched.
Any views shared are strictly my own and do not a represent those of any former employer.
 
tdscanuck
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RE: ILS With Same NAV Freq.? Almost Made Me Crash

Thu Jan 07, 2010 4:51 am



Quoting Wardialer (Reply 3):
So in real flights, when ever this happens and we all know it wont or never has....can this even happen if BOTH ILS CODES or FREQS are enable for that particular runway so the aircraft would just loose control and fall out of the ILS Glideslope????

It won't lose control...worst comes to worst it'll drop out of autoland because, if it grabs the wrong beam, the pointers will go way out of range. At that point, you should go around and get sorted out.

Quoting KELPkid (Reply 4):
Do the avionics in a glass cockpit typically take care of this for you over in part 121 land?

Yes.

Tom.
 
Mir
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RE: ILS With Same NAV Freq.? Almost Made Me Crash

Thu Jan 07, 2010 5:20 am



Quoting Fabo (Reply 8):
In fact, I wonder, if that could work in real life - localizer, if it can transmit both ways, is obviously not a concern, and I guess glideslopes would not interfere, as they point opposite ways?

If you've got two ILS approaches, you have to have two localizers, one for each end. You also have to have two glideslope antennas. One localizer and one glideslope will be active at a time.

-Mir
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IAHFLYR
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RE: ILS With Same NAV Freq.? Almost Made Me Crash

Thu Jan 07, 2010 5:29 am



Quoting Mir (Reply 12):
If you've got two ILS approaches, you have to have two localizers, one for each end.

Not necessarily. The same localizer antenna is capable of working for both runways, just different identifers.
Any views shared are strictly my own and do not a represent those of any former employer.
 
pilotpip
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RE: ILS With Same NAV Freq.? Almost Made Me Crash

Thu Jan 07, 2010 6:40 am



Quoting KELPkid (Reply 4):
Do the avionics in a glass cockpit typically take care of this for you over in part 121 land? I know that identifying navaids (by pulling the little IDENT knobs on the radio stack) is required for GA IFR....I have seen a few cockpit videos of approaches, and it doesn't seem that modern airline aircrews worry too much about the 5 T's and identifying navaids Wink

Yeah, they do. Just like the G-1000. Every now and then (mostly when bored) I reach down to the audio panel and hit the ID button to remember what morse code sounds like.

If you think that's bad, you should see the smoke come out of my ears when I get holding instructions or do a non precision approach...  Smile
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Fabo
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RE: ILS With Same NAV Freq.? Almost Made Me Crash

Thu Jan 07, 2010 8:02 am



Quoting Mir (Reply 12):
One localizer and one glideslope will be active at a time.

Yes, obviously. I am asking though if it were technically possible to have both GS online and usable? Even if for CAT I.
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Mir
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RE: ILS With Same NAV Freq.? Almost Made Me Crash

Thu Jan 07, 2010 10:35 am



Quoting IAHFLYR (Reply 13):
The same localizer antenna is capable of working for both runways

How could it be, since one direction of arrivals would have to fly over the antenna to get to the runway? You'd lose localizer guidance on short final, and the increasing precision as you approached the antenna would make keeping the needle centered very difficult.

Quoting Fabo (Reply 15):
I am asking though if it were technically possible to have both GS online and usable?

I'd imagine it's possible to have them both on, but they would interfere with each other, and as a result neither of them would be usable.

-Mir
7 billion, one nation, imagination...it's a beautiful day
 
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glen
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RE: ILS With Same NAV Freq.? Almost Made Me Crash

Thu Jan 07, 2010 10:49 am



Quoting IAHFLYR (Reply 13):
Not necessarily. The same localizer antenna is capable of working for both runways, just different identifers.

Not true. When using only one antenna you have a backcourse approach. On a traditional CDI-Instrument your left/right indications are vice-versa in this case - even on some modern PFD's unless you can specifiy the backcourse situation in the FMS. An HSI-instrument works fine in this situation when setting the front-course.
Second problem is the fact that on a backcourse approach the antenna is on the approach-side of the runway. This leads to a beam which is much more narrow (an therefore more difficult to follow) at the same distance from runway compared to a approach on the front beam.
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flyinTLow
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RE: ILS With Same NAV Freq.? Almost Made Me Crash

Thu Jan 07, 2010 12:04 pm



Quoting KELPkid (Reply 4):
Do the avionics in a glass cockpit typically take care of this for you over in part 121 land? I know that identifying navaids (by pulling the little IDENT knobs on the radio stack) is required for GA IFR....I have seen a few cockpit videos of approaches, and it doesn't seem that modern airline aircrews worry too much about the 5 T's and identifying navaids Wink

The Airbus A320 identifies NAVaids for you. But it is company policy with most airlines to call out "bla bla bla identified", at least with the ILS.

Cheers,

Thilo
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Glom
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RE: ILS With Same NAV Freq.? Almost Made Me Crash

Thu Jan 07, 2010 12:20 pm



Quoting DiamondFlyer (Reply 5):
The Garmin GNS530 does it, as does their G1000 system. Really makes it almost to easy to do IFR flying today.

Does the G-1000 auto identify or does it simply pluck the ident from the database? I don't know and don't care. I'll always identify beacons. It's just good airmanship. Auto-ident is a complement, not a replacement for manual ident.
 
IAHFLYR
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RE: ILS With Same NAV Freq.? Almost Made Me Crash

Thu Jan 07, 2010 2:00 pm



Quoting GLEN (Reply 17):
Not true



Quoting Mir (Reply 16):
How could it be



Quoting N353sk (Reply 9):
The localizer signal is bi-directional. A Localizer Backcourse approach uses the backside of the localizer signal.

Do you ever make a statement and then wish you'd put about a second more thought into what you really should have said? My apologies folk, you're both correct. I had put two thoughts together into one and it was incorrect!  embarrassed 

Quoting GLEN (Reply 17):
When using only one antenna you have a backcourse approach

Is this the purpose of an interlock switch, to mask the backcourse signal when the localizer is turned around to the other antenna?
Any views shared are strictly my own and do not a represent those of any former employer.
 
Mir
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RE: ILS With Same NAV Freq.? Almost Made Me Crash

Thu Jan 07, 2010 5:17 pm



Quoting IAHFLYR (Reply 20):
Is this the purpose of an interlock switch, to mask the backcourse signal when the localizer is turned around to the other antenna?

I don't think you can mask the backcourse signal. The purpose of the interlock switch should just be to turn one of the localizers and glideslopes off. Let's say you have runway 36 and 18, both with ILS approaches with the same frequency. If you're using 36, you turn off the 18 localizer and glideslope, but the backcourse for 18 (based off of the 36 localizer) is still going to be there. Unless there's a published approach for it, though, nobody is going to be using it (unless it's part of the 36 missed approach procedure, which it could well be - another reason that you wouldn't want to inhibit it even if you could).

Quoting IAHFLYR (Reply 20):
Do you ever make a statement and then wish you'd put about a second more thought into what you really should have said?

All the time.  Smile

-Mir
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AAR90
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RE: ILS With Same NAV Freq.? Almost Made Me Crash

Thu Jan 07, 2010 5:24 pm



Quoting Wardialer (Thread starter):
So my question is, how far out can you enable the NAV/APP switch in order to prevent this "mix-up" which almost made me crash during the approach....????

You used LAX 25L in your example so that is a good example of an ILS with good transmit/reception ranges out beyond 100nm! However, you are not legal to fly the glideslope nearly that far out --although we do monitor it most of the way. I have been cleared to fly the localizer at around 75nm distant though.  Smile

Quoting Wardialer (Thread starter):
Does this happen in real flight???

As you describe it... no. The greater possibility is two different localizers (same freq) from two different (but relatively nearby) airports. Approaching ORD 27L & 28 from the NW we'll see the wrong ID until you get close enough to ORD that their runways' signals become the stronger and the recievers on the plane ID the ORD runways.

Quoting Wardialer (Reply 3):
So in real flights, when ever this happens and we all know it wont or never has....can this even happen if BOTH ILS CODES or FREQS are enable for that particular runway so the aircraft would just loose control and fall out of the ILS Glideslope????

Procedurally, you do not enable the APProach mode of the FD/AP until you have verified reception of the proper ILS by either visual ID (the system does it) and/or aurally (varies by airline & acft). ANYTHING is POSSIBLE, so it is possible to engage APP on the wrong freq. and when the proper freq. becomes the strongest signal, the system will TRY to adjust. Most systems will usually "default" out to HDG HOLD and VERT SPD [out of APP mode] causing the pilot to abandon the approach to sort things out. But procedures & legalities should prevent that since you would not normally be allowed to fly the localizer anywhere near another potential transmitter (on the same freq) and can not (legally) fly the GS until reaching the published "feather" (getting real close to airport). In my ORD example above, the "wrong ID" is found about 100nm away from ORD, but ORD runway IDs are not received until within less than 30nm (usually 20) of ORD [much lower altitude = no reception of other signal].

Quoting KELPkid (Reply 4):
Do the avionics in a glass cockpit typically take care of this for you over in part 121 land? I know that identifying navaids (by pulling the little IDENT knobs on the radio stack) is required for GA IFR....I have seen a few cockpit videos of approaches, and it doesn't seem that modern airline aircrews worry too much about the 5 T's and identifying navaids

Depends upon the system installed. Newer glass cockpit systems have the computers decipher the morse code signal and display the ID visually on the (usually) Nav Display. Older glass cockpits may not do this (think 757/767) or if they did, the airline still required the pilots to aurally ID the station (AA F100/MD90). The 738 is the first AA plane I've flown where aural ID is not required.
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Northwest727
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RE: ILS With Same NAV Freq.? Almost Made Me Crash

Fri Jan 08, 2010 1:34 am

Its just MSFS not being as real as it gets

AIM 1-1-9 Instrument Landing System (ILS) (a)(5):

Quote:
Where a complete ILS system is installed on each end of a runway; (i.e., the approach end of Runway 4 and the approach end of Runway 22) the ILS systems are not in service simultaneously.

http://www.faa.gov/air_traffic/publi...ions/ATpubs/AIM/Chap1/aim0101.html
 
FredT
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RE: ILS With Same NAV Freq.? Almost Made Me Crash

Fri Jan 08, 2010 5:20 pm

When both ILS'es are on the same frequency, they are to be interlocked so that they cannot both be switched on at the same time. The tower has to select one.

However, if one system is put in maintenance mode, that feature is bypassed. Having both on creates an interesting signal for sure.

Quoting Mir (Reply 21):
I don't think you can mask the backcourse signal.

You can suppress it significantly, and in my experience it is the norm i e by having a reflector at the dead side of the antenna or using log-dipoles. Why radiate energy the wrong way for no use at all? In large parts of the world, back course approaches are not allowed anyway.

BTW, glide paths can and sometimes do have perfectly flyable back courses... but don't expect them to be pretty. And, of course, they end up at the wrong end of the runway... Big grin
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KELPkid
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RE: ILS With Same NAV Freq.? Almost Made Me Crash

Fri Jan 08, 2010 6:52 pm

Quoting AAR90 (Reply 22):
Older glass cockpits may not do this (think 757/767 or if they did, the airline still required the pilots to aurally ID the station )

Doubly so, probably over at AA. Wasn't the Cali, Colombia accident caused, in part, by tuning to the wrong navaid? I know it was also a situational awareness type of accident...the flight crew wasn't where they thought they were.

[Edited 2010-01-08 10:54:59]
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XFSUgimpLB41X
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RE: ILS With Same NAV Freq.? Almost Made Me Crash

Fri Jan 08, 2010 8:41 pm

Quoting KELPkid (Reply 25):
Doubly so, probably over at AA. Wasn't the Cali, Colombia accident caused, in part, by tuning to the wrong navaid? I know it was also a situational awareness type of accident...the flight crew wasn't where they thought they were.

It was an FMC waypoint selection error, not tuning the wrong navaid. When you select a waypoint from the database, say "CRG" (desiring "Craig" VOR near jacksonville, FL), there are actually about 4 navaids around the world with the same 3 letter identifier. You have to look at the lat/long next to the choices and make sure you're picking the right one.

The Cali Columbia guys picked the wrong one which turned the aircraft into the hills... Always remember to fly the plane!




In the 757/767, when flying an ILS or VOR approach, you have to identify the frequency aurally.

The CRJ would "listen" to the freq and, once it got a good ID, put it up on the PFD.

[Edited 2010-01-08 12:42:07]

[Edited 2010-01-08 12:43:14]
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AAR90
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RE: ILS With Same NAV Freq.? Almost Made Me Crash

Fri Jan 08, 2010 9:13 pm



Quoting KELPkid (Reply 25):
by tuning to the wrong navaid?

They selected "R" radio beacon and the FMS presented 2 pages of "R" waypoints. They chose the first one on the list (thinking it was closest?) which was actually behind the acft quite a distance. The mishap was caused (amongst other items) by allowing the plane to fly in a turn for (IIRC) 90+ seconds while descending between two ridgelines (into a valley). I would never allow that to happen, but that's because I don't regularly fly into such terrain. Were I one of those crewmembers who regularly flew to Cali..... who knows?! [but I hope I wouldn't have made such a basic mistake]. Still, not quite the same ID'ing issue.

Quoting XFSUgimpLB41X (Reply 26):
In the 757/767, when flying an ILS or VOR approach, you have to identify the frequency aurally.

That's the procedure AA used when I flew the 757/767 fleet. Not sure if the new MAUI birds will see the NAVAID ID displayed or not, but it will be quite some time before the entire fleet is converted, so expect to see AA procedures remain aural ID for 757/767 for a few more years at least.
*NO CARRIER* -- A Naval Aviator's worst nightmare!
 
Mir
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RE: ILS With Same NAV Freq.? Almost Made Me Crash

Fri Jan 08, 2010 10:29 pm



Quoting KELPkid (Reply 25):
Wasn't the Cali, Colombia accident caused, in part, by tuning to the wrong navaid? I know it was also a situational awareness type of accident...the flight crew wasn't where they thought they were.

It was an improper FMC selection. They wanted to go to the Rozo NDB, which has the code R. So they typed in R into the FMC, picked the first one that came up (the closest one), and let the plane take them to it while they tried to figure out what they were doing. Problem was that they had selected an NDB near Bogota - the Rozo NDB was in the database as ROZO (in order to prevent confusion with the very NDB that they had selected).

It's easy to get confused by something like that if you don't know how the FMC logic works, but one always has to look at what the airplane is going to do before you execute a change like that. You'll see a proposed flight path on the map display - this is the airplane's way of saying "this is what I'm going to do if you push that Execute button, are you sure that's what you want?"

There are a lot of other causes involved (failure to retract the speedbrakes during the terrain escape maneuver, etc.), but the three big ones in my mind are the crew's acceptance of an approach that they didn't have enough time to properly set up for, the crew's failure to maintain positional awareness, and the crew's decision to let the FMC fly the airplane.

-Mir
7 billion, one nation, imagination...it's a beautiful day

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