rotation18L
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Joined: Sat Jun 23, 2001 11:30 am

Vasi V Localizer

Sun May 13, 2007 12:03 am

I have always wondered this:

At some airports, why do runways that face the same direction, side-by-side, have VASI on one runway as the approach and use a localizer on the parallel runway? Why don't both runways use one or the other? For that matter, since using ILS is probably easier (I'm not a licensed pilot, but I did fly with a CFI once and watched the VASI as he made the landing, yet I've never flown either), why even use VASI at airports where a localizer is available?

Just curious  boggled 
 
pilotpip
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RE: Vasi V Localizer

Sun May 13, 2007 12:36 am

First you have to understand what each does. A localizer provides lateral guidance. Visual Approach Slope Indicators (VASI) provides vertical guidance. Not all airports have these. Many airports don't have an ILS or localizer approach but many have visual indicators like a VASI or PAPI. They are relatively low cost when compared to the costs associated with an ILS.

A VASI is nice but I will often take my students to airports without them intentionally. Runway makings and other cues work just as well and they need to be competent to land without these. In fact, most people won't even know how to do an ILS until they start on their instrument rating. VFR charts don't list the frequencies for them as it is.
DMI
 
Goldenshield
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RE: Vasi V Localizer

Sun May 13, 2007 12:45 am

Here's a good read on VASI, their use, and their limitations:

Link to the appropriate section of the Airman's Information Manual

Fair use excerpt: (But since it's a government publication, I could legally copy the whole thing.)

1. The VASI is a system of lights so arranged to provide visual descent guidance information during the approach to a runway. These lights are visible from 3-5 miles during the day and up to 20 miles or more at night. The visual glide path of the VASI provides safe obstruction clearance within plus or minus 10 degrees of the extended runway centerline and to 4 NM from the runway threshold. Descent, using the VASI, should not be initiated until the aircraft is visually aligned with the runway. Lateral course guidance is provided by the runway or runway lights.
Two all beef patties, special sauce, lettuce, cheese, pickles, onions on a sesame seed bun.
 
Mir
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RE: Vasi V Localizer

Sun May 13, 2007 1:17 am

I've heard that VASIs are more common than PAPIs on runways with ILS systems, since VASIs count as one of the elements you need to see to continue below minimums and PAPIs do not.

-Mir
7 billion, one nation, imagination...it's a beautiful day
 
KELPkid
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RE: Vasi V Localizer

Sun May 13, 2007 1:19 am

Well, first-off, the appropriate analogy would be the glideslope (not the localizer) versus the VASI...

Second, many times the VASI is pretty close to the localizer, although I have seen on a few approach plates here in the Pacific Northwest a caution that the VASI and the glideslope aren't coincidental.

Quoting Rotation18L (Thread starter):
For that matter, since using ILS is probably easier (I'm not a licensed pilot, but I did fly with a CFI once and watched the VASI as he made the landing, yet I've never flown either),

definitely *NOT* the case. Hand flying an ILS is much more difficult than tracking the VASI on final...but if you are in a significantly automated cockpit, you can "push button, fly the glideslope and localizer", although unless it's a Cat IIIC, you have to intervene for the flare and landing.

Quoting Rotation18L (Thread starter):
why even use VASI at airports where a localizer is available?

Simple: the VASI is a visual landing aid, and the glideslope isn't. If you are shooting a visual approach, you go with the appropriate system...

Also, on a typical Cat I runway, the performance of the glideslope is only guaranteed down to the decision altitude. You simply cannot depend on the glideslope below that...even if it's a Cat II or Cat III runway, descending below the Cat I minimums requires both flight crew and aircraft certification (read:expensive equipment for GA), so ILS'es below Cat I minimums are rare for general aviation to say the least...although I'm sure a few bizjets and their aircrew are certified for Cat II or Cat III  Smile
Celebrating the birth of KELPkidJR on August 5, 2009 :-)
 
pilotpip
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RE: Vasi V Localizer

Sun May 13, 2007 1:36 am

Quoting Mir (Reply 3):
I've heard that VASIs are more common than PAPIs on runways with ILS systems, since VASIs count as one of the elements you need to see to continue below minimums and PAPIs do not.

-Mir

They are both forms of visual approach path indicators. Either one can be used on a runway with an ILS approach.
DMI
 
atct
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RE: Vasi V Localizer

Sun May 13, 2007 2:28 am

PAPI's are used in conjuction with precision approaches hence the "Precision Approach Path" vs the VASI which would be "Visual Approach" etc. We had a VASI at Rostraver Airport (FWQ) but no precision approach. (just a VOR-A / RNAV)

Here at IAH we have PAPI's in conjuction with MALSR's / ALSF and the ILS's, but then again, most of our traffic is Cat II or better equipped/trained. We dont get many C172's (Ive seen one) in and out often on the ILS.

ATCT
Trikes are for kids!
 
Fly2HMO
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RE: Vasi V Localizer

Sun May 13, 2007 4:23 am

Quoting Pilotpip (Reply 5):
They are both forms of visual approach path indicators. Either one can be used on a runway with an ILS approach.

True that.

Quoting ATCT (Reply 6):
PAPI's are used in conjuction with precision approaches hence the "Precision Approach Path" vs the VASI which would be "Visual Approach" etc.

True that again. Here in PRC, rwy 21L and 3R (with ILS) have 4 light PAPIs. All the other runways have 2 light PAPI installations IIRC.

The most interesting one is the Tricolor VASI. Only ran into one once, in Needles, CA.
 
IAHFLYR
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RE: Vasi V Localizer

Sun May 13, 2007 8:27 am

Quoting KELPkid (Reply 4):
...although I'm sure a few bizjets and their aircrew are certified for Cat II or Cat III

I know of a C421 that has CATIII certification as well as the owner, that is a case of someone having way more money than sense!!  Smile

Quoting ATCT (Reply 6):
Cat II or better equipped/trained.

Except the CHQ crews now showing up at IAH....my guess is they need to determine the cost benefits and wish they'd hurry up and do that!

Quoting ATCT (Reply 6):
We dont get many C172's (Ive seen one) in and out often on the ILS.

The guy who does that trip only does it to piss of the traffic management folks.  Cool

So of PAPI or VASI systems, which is aligned with the average flight deck height????  Smile
Any views shared are strictly my own and do not a represent those of any former employer.
 
Fly2HMO
Posts: 7207
Joined: Sat Jan 24, 2004 12:14 pm

RE: Vasi V Localizer

Sun May 13, 2007 4:29 pm

Quoting Iahflyr (Reply 8):
So of PAPI or VASI systems, which is aligned with the average flight deck height????

I've read somewhere (AIM?) that the larger heavies sometimes are required to fly a slightly steeper approach i.e. 3 white PAPIs or, in the case of a three light VASI, one red over two white.

And I know the average GS is 3 deg, but are they considering average cabin height? No clue.

And while we're at it, does anybody know of any "T" VASI (not tricolor) pics on the database? I think Australian airports usually have these but I haven't found any pics yet.
 
atct
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RE: Vasi V Localizer

Mon May 14, 2007 3:37 am

Quoting Iahflyr (Reply 8):
The guy who does that trip only does it to piss of the traffic management folks.

I have no idea of whom you speak of....Id never fly a single into IAH.....  devil 

(Once i get a bird...ive actually thought of commuting in one on nice days...like the guy with the RV-6 and the CAL guy in his Bonanza)

ATCT
Trikes are for kids!
 
Fly2HMO
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RE: Vasi V Localizer

Mon May 14, 2007 6:47 am

Quoting Iahflyr (Reply 8):
The guy who does that trip only does it to piss of the traffic management folks.

I am one of those guys at PHX every once in a while.  mischievous 

Usually they're cool about it, and what I do is fly around balls to the wall throughout the approach without them having to tell me because I know they would request best forward speed anyways. Heck, one time I was even passing a WN plane coming in on the parallel. And I was in a little putt-putt Seminole doing the "202 approach" (Vne on the PA 44 is 202kias  Big grin ) .

They usually thank me for being expeditious over the radio.
 
Mir
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RE: Vasi V Localizer

Mon May 14, 2007 12:13 pm

Quoting FLY2HMO (Reply 9):
And I know the average GS is 3 deg, but are they considering average cabin height? No clue.

I don't think that they are. I know that they do for aircraft carriers, and will recalibrate the meatball for each particular aircraft type, but that kind of thing calls for a lot more precision than a standard runway.

-Mir
7 billion, one nation, imagination...it's a beautiful day
 
pilotpip
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RE: Vasi V Localizer

Mon May 14, 2007 12:15 pm

Quoting FLY2HMO (Reply 9):
And I know the average GS is 3 deg, but are they considering average cabin height? No clue.

They are usually 3 degree, yes. However they aren't adjusted for cabin height. There are three-row VASIs out there however. The top is for viewing from a tall plane, the bottom is for smaller aircraft.
DMI
 
rotation18L
Posts: 32
Joined: Sat Jun 23, 2001 11:30 am

RE: Vasi V Localizer

Tue May 15, 2007 9:02 am

Thanks for your responses. Very interesting.

So, the decision to use ILS or VASI (or PAPI) depends on whether you want to make a visual approach or not? Is that why some runways are equipped with VASI (PAPI) only while others are not (at the same airport or just in general? What caught my attention about this topic are two runways at MCO: 18L uses VASI while 18R does not. It's ILS-equipped. So suppose you're flying VFR, don't have ILS equipment and are vectored to 18R? What do you do?)


Does that mean that runways not equipped with VASIs/PAPIs would not be used by pilots doing visual approaches? (SincePilotpip mentioned in this thread that runway markings can be used for visual approaches just as effectively, I would assume that if you were on final for an "ILS only" runway w/o VASI or PAPI aids, and you were flying VFR, you would use these runway markings as your guidance, is this correct?)

I guess what I'm getting at is, what dictates whether you do a visual approach or precision approach? I assume if you're flying VFR, you wouldn't be doing an ILS approach, correct? Also, I assume that low visibility would dictate that you do not do a visual approach for obvious reasons, even if you're flying IFR?

(And by the way, I did some add'l reading based on your suggestions, and see that I was erroneously referring to "localizer" as ILS, as if the two were interchangeable terms. I see that they are not, and that "localizer" refers to an ILS component. Thanks for clarifying that.)

Sorry for the basic questions. At this point, I'm a pilot wannabe.  yes 
 
IAHFLYR
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RE: Vasi V Localizer

Tue May 15, 2007 9:39 am

Quoting Rotation18L (Reply 14):
Sorry for the basic questions. At this point, I'm a pilot wannabe.

Well good for you. most of us on here who are in the industry either professionally or for fun enjoy hearing from those who are starting out......you go pal!

I'll attempt to help answer some of your questions in your last post later as I have been summonsed to the grill for the evening, bet someone beats me to it however!  Smile
Any views shared are strictly my own and do not a represent those of any former employer.
 
pilotpip
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RE: Vasi V Localizer

Tue May 15, 2007 10:59 am

There are two basic weather conditions that we fly in. Visual Meteorlogical Conditions (VMC) and Instrument Meteorlogical Conditions (IMC). In the first, we are flying in condtions where visibility is good enough to look outside and keep ourselves from hitting stuff. In IMC, as the name implies, we are flying in visibility that is low enough that we're relying on our instruments to keep us in the air and guys like ATCT to keep us from hitting each other.

People often confuse IMC with Instrument Flight Rules (IFR). There are two basic sets of rules that we can fly by. Visual Flight Rules (VFR) allow us to fly when the weather is nice, or in VMC. IFR allows us to fly in poor weather or IMC. We can file an IFR flight plan in VMC or IMC, but under VMC conditions we are still responsible for not running into stuff while being vectored around. Confused yet? It should be clear as mud  Smile

In IMC we need approach procedures to guide us to the runway. There are a variety of these, ILS being one of them. It's also the only one that provides vertical guidance (before somebody corrects me, I'm keeping it simple). As a result, we can fly these to lower cloud ceilings and visiblities. The other ones only provide lateral guidance.

One thing remains constant, when you "break out" you transition to hte visual phase of landing. You fly the plane to the runway using your eyes and land. This is one of the cornerstones of flying and also one of the most difficult tasks you'll encounter early and often if you decide to train towards a private certificate. Visual Approach Slope Indicators (VASI) and Precision Approach Path Indicators (PAPI) are there to aid in this visual portion. They are typically 3 degree descent angles but not always and may be adjusted for things such as terrain.

So what if we don't have a VASI or PAPI? Or for that matter, what if there's something preventing us from a 3 degree descent? What if the runway is short and we want to get on the ground as close to the end and stop as fast as possible? We want to come in steeper and slower to do that. We use our eyes and judge for ourselves. We can look at the runway, and judge if we are on the proper descent or if adjustments need to be made. This is one of my primary jobs as an instructor, teaching my students how to do this.

Yeah, this is pretty long winded. You sound like you have a great intrest learning to fly. I'd suggest heading out to your local flight school and signing up for a ground school. They usually aren't too expensive in the grand scheme of flight training. The FAA also publishes a number of training manuals. They're a little dry but contain all of this information and through the magic of the Freedom of Information Act they're all available on the FAA website in PDF format. I'd suggest the "Pilot's Handbook of Aeronautical Knowledge" and the "Airplane Flying Handbook". Those are the cornerstone of our training. Hope this gives a little insight.
DMI
 
IAHFLYR
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Joined: Sat Jun 25, 2005 12:56 am

RE: Vasi V Localizer

Tue May 15, 2007 8:23 pm

Quoting Pilotpip (Reply 16):

Very well done.....  bigthumbsup 
Any views shared are strictly my own and do not a represent those of any former employer.
 
rotation18L
Posts: 32
Joined: Sat Jun 23, 2001 11:30 am

RE: Vasi V Localizer

Wed May 16, 2007 10:44 am

Quoting Pilotpip (Reply 16):
You sound like you have a great intrest learning to fly

I do. If I can get past the nausea, I think I'll be good to go! That's my biggest roadblock at this point. vomit 

Thanks for taking the time to answer my questions!  Smile
 
pilotpip
Posts: 2820
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RE: Vasi V Localizer

Wed May 16, 2007 12:29 pm

I got a little airsick my first couple flights. The anticipation and excitement didn't help.

Things that I suggest that usually work:

1) Eat. Most people think an empty stomach is better, but not the case. Eat a light meal a couple hours before.
2) Look outside, at the horizon. Private pilots are supposed to be outside of the airplane 90% of the time. Staying inside messes with your head.
DMI

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