Simviation Forum - Bad weather and no glide slope.

Dec 29^th, 2008 at 7:08pm

Rocket_Bird Offline
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Canada

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The ILS is really a luxury when it comes to landing in near zero visibility, low ceilings, and poor weather. But what happens when an airport lacks a glide slope or if the glide slope is not working? I was watching an episode of Air Crash Investigation few nights ago when I saw that in 1997, a 747 on its way to land in Guam crashed because of a combination of sleep deprivation, pilot error, bad weather, and missing glide slope. In such conditions, I would think that a working glide slope would really have made the difference, though I am certain that most if not all instrument pilots receive some training to deal with such situations.

I was flightsimming a little time after, flying the PMDG 744 to Rome I think when I encountered similar conditions: rain, low visibility, low ceiling, and no glide slope (for that side of the runway just had a localizer). Give me a glide slope, and I'll land the plane, but I really don't run into this often. With luck, and with the comfort that flight simulator is in the safety of my own home, I managed to catch sight of the runway at 500 feet and land safely. Still, even if such conditions are rare--depending on where you normally fly--it raised this question for me; how do you properly land a plane in instrument conditions when you have nothing to go on except maybe a DME and a localizer?

I remember seeing on that one episode of ACI that pilots normally (or at least, "should") "step down" to prescribed altitudes in conditions such as that mentioned above. I examined a few approach plates at various airports and could not really find much information on "prescribed altitudes." I'm sure there is a way to calculate what height I need to be at what distance from the airport, but how do I do this? I know there is a little box at the bottom of most approach plates that lists time and knots as an indicator to distance. . . would I use this to calculate my descent? How do instrument and ATP pilots handle normally handle a situation such as this?

Cheers,
RB

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Reply #1 - Dec 29^th, 2008 at 8:40pm

C Offline
Colonel
Earth

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Rocket_Bird wrote on Dec 29^th, 2008 at 7:08pm:

The ILS is really a luxury when it comes to landing in near zero visibility, low ceilings, and poor weather. But what happens when an airport lacks a glide slope or if the glide slope is not working? I was watching an episode of Air Crash Investigation few nights ago when I saw that in 1997, a 747 on its way to land in Guam crashed because of a combination of sleep deprivation, pilot error, bad weather, and missing glide slope. In such conditions, I would think that a working glide slope would really have made the difference, though I am certain that most if not all instrument pilots receive some training to deal with such situations.

I was flightsimming a little time after, flying the PMDG 744 to Rome I think when I encountered similar conditions: rain, low visibility, low ceiling, and no glide slope (for that side of the runway just had a localizer). Give me a glide slope, and I'll land the plane, but I really don't run into this often. With luck, and with the comfort that flight simulator is in the safety of my own home, I managed to catch sight of the runway at 500 feet and land safely. Still, even if such conditions are rare--depending on where you normally fly--it raised this question for me; how do you properly land a plane in instrument conditions when you have nothing to go on except maybe a DME and a localizer?

I remember seeing on that one episode of ACI that pilots normally (or at least, "should") "step down" to prescribed altitudes in conditions such as that mentioned above. I examined a few approach plates at various airports and could not really find much information on "prescribed altitudes." I'm sure there is a way to calculate what height I need to be at what distance from the airport, but how do I do this? I know there is a little box at the bottom of most approach plates that lists time and knots as an indicator to distance. . . would I use this to calculate my descent? How do instrument and ATP pilots handle normally handle a situation such as this?

Simple. You fly a published non-precision approach, be it a Localizer based approach, or using another non precision aid such as NDB, VOR or a TACAN. With the luxury of DME, a 3 degree glidepath will have you 1500ft AGL at 5 miles, so you can roughly work on 300ft/nm. Of course, as you mention, you have to adhere to any step heights etc, and have a minimum descent altitude/height as opposed to a decision altitude or height.

Have a "cast iron" diversion airfield up your sleeve too, just in case you can't see the lights.

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Reply #2 - Dec 29^th, 2008 at 8:47pm

-Crossfire- Offline
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A LOC approach does use step down altitudes, just like an NDB, or any other non-precision approach. A non-presicision approach is basically any approach without a glideslope. A LOC/DME approach, for example, will have specific altitudes that you should be at along with coordinating DME distances. The timing is used to figure out when to start the missed approach. On a non-precision approach, you should be at the MDA (minimum decent altitude) before your timing is up, so you will have a good shot at seeing the runway in bad weather conditions.

Hope this helps. Cool

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Reply #3 - Dec 29^th, 2008 at 9:07pm

Rocket_Bird Offline
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Thank you! I had just dug out some non precision approach charts and have found the procedures there. For some reason, it didn't even occur to me to look into those charts (I don't get exposed to them often Cheesy

). The 1500 ft AGL at 5 miles is helpful also--at least for the lazy flight simmer who doesn't always look at his charts Wink

.

Cheers,
RB

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Reply #4 - Dec 29^th, 2008 at 9:25pm

Brett_Henderson Offline
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BE AN NDB

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This is gooood stuff (and inspiring me to get busy on the IFR lessons)..

You guys have covered non-precision approaches pretty well.. so there's not much to add... Other than the obvious.. that a non-precision approach would have a higher MDA.. an under real world conditions (if you obey minimums), you catch sight of the runway, well before getting into trouble.

The interesting thing that's rarely talked about, on step-down descents, is that you do not have maintain a constant glide-path. It certainly makes it easier and safer (because it requires a stabilized approach), but as soon as you pass any of the, "descend no lower before" fixes..you can dive to the next altitude, and then fly level, waiting on the next.

The only reason I bring this up, is that in the common IFR training aircraft, you're talking about something pretty small and slow (and forgiving). It's not so much that you end up descending early on purpose, but it's more like a learned response. I'll promise you, that the first time you shoot n NDB approach (if the CFI lets you lern by making a mistake), you'll come in high... VERY high. After a couple of those, you'll find yourself rushing the descent.. and you kinda learn by reward that it's not a bad way to fly the approach (in a FORGIVING, slow airplane). You're not only down to DH sooner.. you get stable there, and the likelyhood of accidentally dropping too low is lessened.

As for no glideslope.. I'd almost rather have a DME. Obvioulsy BOTH would be better.. but of the two.. I've found that chasing a needle is more problematic than just establishing a stabilized approach, and then referencing your agl by DME... because by non-precision minimums, you won't be cutting it that close, anyway.

Today though.. even a lowly, rental C172 is likely to be GPS equiped. GPS approaches take all the "fun" out of it.. Our club has two Warriors, and one Skyhawk with Garmin 430s installed.. and they're all WAAS capable .. pretty much a precision approach for ever runway in the world Cool

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Reply #5 - Dec 30^th, 2008 at 1:15am

Rocket_Bird Offline
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Canada

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Thanks for sharing. After looking at some of these non-precision plates, I'm starting to see some of the benefits of flying such approaches. It is quite nice to be able to perform a precision approach, but when it comes down to the above conditions, things do become quite a bit more. . . fun.

Cheers!

Cheers,
RB

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Reply #6 - Dec 30^th, 2008 at 4:36am

pepper_airborne Offline
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Voorhout - The Netherlands

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Good reading material here guys, thanks!!

http://white-line.org/&&;

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Reply #7 - Dec 30^th, 2008 at 6:23am

C Offline
Colonel
Earth

Posts: 13144

Brett_Henderson wrote on Dec 29^th, 2008 at 9:25pm:

The interesting thing that's rarely talked about, on step-down descents, is that you do not have maintain a constant glide-path. It certainly makes it easier and safer (because it requires a stabilized approach), but as soon as you pass any of the, "descend no lower before" fixes..you can dive to the next altitude, and then fly level, waiting on the next.

Indeed, although after certain incidents (Iran Air at Birmingham in the UK, trucking it from about 10miles at 700ft!) the word "notional glidepath mandatory" are appearing more and more. Eventually of course, with better and better autopilots, aircraft will just fly a non-precision approach as if it is a precision.

R_B: As you may have noticed, the Loc/Loc-DME procedure is normally on the same plate as the ILS.

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Reply #8 - Dec 30^th, 2008 at 6:04pm

Mobius Offline
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Highest Point in the Lightning
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Wisconsin

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Now also, with the introduction of WAAS enabled GPS systems, you can make an approach into almost any airport with a glideslope. I think the DA is still higher than an ILS approach though, but I could be mistaken as I've never actually flown a VNAV approach. Tongue

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Reply #9 - Dec 30^th, 2008 at 6:42pm

C Offline
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Earth

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Mobius wrote on Dec 30^th, 2008 at 6:04pm:

Now also, with the introduction of WAAS enabled GPS systems, you can make an approach into almost any airport with a glideslope. I think the DA is still higher than an ILS approach though, but I could be mistaken as I've never actually flown a VNAV approach. Tongue

I wonder how it will catch on though. I may have mentioned this recently, but going through my old magazines. I came across a 1997 issue of "Pilot". In the news section it mentioned how the FAA expected most VORs to be obsolete within a decade... Shocked

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Reply #10 - Dec 30^th, 2008 at 7:52pm

Mobius Offline
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Highest Point in the Lightning
Storm
Wisconsin

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C wrote on Dec 30^th, 2008 at 6:42pm:

Mobius wrote on Dec 30^th, 2008 at 6:04pm:

Now also, with the introduction of WAAS enabled GPS systems, you can make an approach into almost any airport with a glideslope. I think the DA is still higher than an ILS approach though, but I could be mistaken as I've never actually flown a VNAV approach. Tongue

I wonder how it will catch on though. I may have mentioned this recently, but going through my old magazines. I came across a 1997 issue of "Pilot". In the news section it mentioned how the FAA expected most VORs to be obsolete within a decade... Shocked

They've actually stopped maintaining some VORs over here, and there is at least one WAAS approach into most airports, even my home airport: http://204.108.4.16/d-tpp/0813/06171R28.PDF ; Wink

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Reply #11 - Dec 30^th, 2008 at 9:17pm

Brett_Henderson Offline
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EVERY OUTER MARKER SHOULD
BE AN NDB

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Wellll.. VORs are obsolete.. have been for years now. The equipment on the ground is a maintanence head-ache.. and the equipment in the airplane is too.. not to mention expensive and heavy (and notoriously innaccurate).

They'll linger on though.. kinda like lighthouses, in the GPS dominated maritime world. Old and clunky security blankets.. lol

As for GPS approaches.. there is an interesting oleo in the data-base. There are the genuine GPS approaches, that are largely, logical 'T' formations.. relying on fixes that only a GPS can avail. And there are a good chunk of the old, 'standard' approaches.. precision and non-precision. That's a bad mix of GPS companies having to live within ancient, slow-moving, government agencies, like the FAA.

ANYway.. The bad thing about 'non GPS', GPS approaches, is that they induce a level of laziness and complacency, and even daring. Pilots file for say, an ILS, and then end up flying a bastardized version of it; relying more on the GPS, than the ILS gauge (after all .. who needs to worry about overshooting the turn to final when ATC is vectoring you). Think about it. You've got a moving map for dead-on accurate, position awareness. And a ridiculously accurate "DME". I'll admit myself, to plowing ahead and descending into IMC after talking to someone at an FBO. He confirmed there was indeed a hard ceiling at 500agl, but once below it, the visibiity was easily 3 miles. Question to myself..

"Do I fly in circles up here.. VFR on top; trying to reach an approach control to file an instrument approach on the go (which would have entailed flying several miles, because climbing for reception was out of the question ?).. Or.. do I just improvise a GPS approach ? "...

I chose to improvise. Knowing that you're flying at the runway on perfect runway heading.. with a perfectly accurate "DME", and a perfectly functioning altimeter.. and knowing by verbal confirmation that conditions under the overcast layer were good.. flying that approach was safer than groping around in the clouds for an IFR clearance, or a VFR alternate. And of course, it went off like clockwork.. Watch the GPS screen as part of your scan using that as your localizer.. check your altitude against the distance to the the runway.. Sure enough, I popped out at 500agl, just over a mile from the runway.. perfect VFR landing .

The point I'm trying to make by admiting to that violation.. is that instrument training needs to evolve.. and Instrument Flight Rules need to be adapted to the new equipment... Along with a tightening of the requirements and proficiency displayed in order to GET an instrument rating. The average pilot who will need to use his instrument skills (above and beyond a routine, filed flight) should have in his mental tool bag; not only the skill to shoot the approach I just mentioned, but the authority to make that call. To date, instrument tickets have been pretty much given to anyone who trained for them. Everyone knows that 99/100 filed approaches will have ATC holding your hand until you turn final. Meaning most instrument pilots rarely ever have to even glance at the plate (that they don't have on their lap) (and probably forgot how to read by glance alone, anyway)..

Did I just hi-jack this thread from within the post ? Tongue

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Reply #12 - Jan 6^th, 2009 at 11:56pm

-Crossfire- Offline
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Northern Canada

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Brett_Henderson wrote on Dec 29^th, 2008 at 9:25pm:

Today though.. even a lowly, rental C172 is likely to be GPS equiped. GPS approaches take all the "fun" out of it.. Our club has two Warriors, and one Skyhawk with Garmin 430s installed.. and they're all WAAS capable .. pretty much a precision approach for ever runway in the world Cool

You guys are spoiled in the US!! I did all my IFR training on the Pacific Coast of BC in a Garmin 530W-equipped Piper Twin Comanche, and I have never done a LPV WAAS approach, because none of the airports around here have them. All I've done is LNAV and LNAV/VNAV GPS approaches.

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Reply #13 - Jan 21^st, 2009 at 5:48pm

flaminghotsauce Offline
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I love YaBB 1G - SP1!

Posts: 181

Brett_Henderson wrote on Dec 29^th, 2008 at 9:25pm:

This is gooood stuff (and inspiring me to get busy on the IFR lessons)..

You guys have covered non-precision approaches pretty well.. so there's not much to add... Other than the obvious.. that a non-precision approach would have a higher MDA.. an under real world conditions (if you obey minimums), you catch sight of the runway, well before getting into trouble.

The interesting thing that's rarely talked about, on step-down descents, is that you do not have maintain a constant glide-path. It certainly makes it easier and safer (because it requires a stabilized approach), but as soon as you pass any of the, "descend no lower before" fixes..you can dive to the next altitude, and then fly level, waiting on the next.

The only reason I bring this up, is that in the common IFR training aircraft, you're talking about something pretty small and slow (and forgiving). It's not so much that you end up descending early on purpose, but it's more like a learned response. I'll promise you, that the first time you shoot n NDB approach (if the CFI lets you lern by making a mistake), you'll come in high... VERY high. After a couple of those, you'll find yourself rushing the descent.. and you kinda learn by reward that it's not a bad way to fly the approach (in a FORGIVING, slow airplane). You're not only down to DH sooner.. you get stable there, and the likelyhood of accidentally dropping too low is lessened.

As for no glideslope.. I'd almost rather have a DME. Obvioulsy BOTH would be better.. but of the two.. I've found that chasing a needle is more problematic than just establishing a stabilized approach, and then referencing your agl by DME... because by non-precision minimums, you won't be cutting it that close, anyway.

Today though.. even a lowly, rental C172 is likely to be GPS equiped. GPS approaches take all the "fun" out of it.. Our club has two Warriors, and one Skyhawk with Garmin 430s installed.. and they're all WAAS capable .. pretty much a precision approach for ever runway in the world Cool

I'm kind of late to this thread, but there's another VERY good reason to do the non-precision approach "step altitudes". Assuming an ILS is available as well as a non-precision approach, an ILS will keep you in ice inducing clouds longer than a rapid decent to the next "step". If you know the clouds are going to clear and you're picking up ice, DO get out of the ice. My Chief Flight instructor, and at least two of the regular instructors encountered these situations, and were impressed enough to mention it. One of my instructors apparently had enough ice on an airframe that he had to fly into the runway nearly full throttle to prevent the stall.

ICE is nasty.

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