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Mr Spaceman
Topic Author
Posts: 2723
Joined: Thu Mar 15, 2001 5:09 am

A Question About Fog And An Apology.

Thu Nov 27, 2003 5:10 am

Hi guys.

First off, I want to apologize to all the members who responded to my last questions about holding patterns, Cessna 310 nose intakes and mobile crew rests. I didn't post back because I was very sick & in the hospital. I'm very sorry about that.

Ok. on with the show!

Back in September on a very foggy morning (thick pea soup) I was listening to my receiver and could hear that Westjet 737's were unable to land at Hamilton Airport (YHM) which is a major hub for them. The pilots were attempting approaches, but were having to overshoot and divert to Ottawa Intl.

Then after the ATC arrival controller cleared another Westjet 737 for the ILS into Hamilton, he also stated ....."a heavy is about to start rolling. Hopefully he'll clear away some of the fog for you. That might help you get in".

To which the pilot responded "yeah, let's hope so."

I found this conversation very interesting.

At that time I don't know what the runway visual range (RVR) was, however, about a half hour later it was reported by the controller as 5000 feet.

My question is .........

How often do airline pilots on final approach in heavy fog hope the jet blast from a previous jet's takeoff will help them see the threshold environment?

Can a airliner's jet blast improve a runway's RVR to the point where it can determine whether or not an arriving aircraft can continue the approach past the DH or go around?

Have any pilots out there benefited from another aircraft's jetblast while landing or departing on a foggy day?

If fog dispersal systems beside runway thresholds can work, then I guess an airliner's jet blast couldn't hurt.


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Thanks,

Chris  Smile
 
flightsimfreak
Posts: 698
Joined: Sun Oct 29, 2000 9:36 am

RE: A Question About Fog And An Apology.

Thu Nov 27, 2003 5:21 am

Sounds almost like sarcasm to me. I doubt the controller really thought that it would help... Just some friendly joking between the two.
 
Guest

RE: A Question About Fog And An Apology.

Thu Nov 27, 2003 5:28 am

Fog is created when ambient temperature decreases to the dew point temperature.
When an airplane rolls with its full power on a runway, the air temperature goes up because of jet engines exhaust... result is - fog is reduced...
Some airports have done this - install an old jet engine on a trailer or truck, and run it along the runways to attempt to increase the temperature/dew point spread. It really works, but works... a little, and depends on other local conditions... I have seen a Cavarelle in the early 1970s accelerating on the runway, then going in reverse, to assist other company airplanes to get a better RVR... then that Caravelle coming back, ready for takeoff...
xxx
Happy contrails  Smile
(s) Skipper

 
Mr Spaceman
Topic Author
Posts: 2723
Joined: Thu Mar 15, 2001 5:09 am

RE: A Question About Fog And An Apology.

Thu Nov 27, 2003 5:41 am

Hi guys.

> FlightSimFreak, I understand why you or anyone might think that the controller was just throwing in some sarcasm to help deal with the lousy weather, however, I listen to this controller all the time and I'm very sure that his comment was serious.

> B747Skipper, that's a pretty neat story about the Cavarelle back in the 70's trying to help improve the runway RVR for a company aircraft.

There's photos of fog dispersal systems embeded in the ground at some airports in the database. I just have to find them.

Chris  Smile
 
avt007
Posts: 1989
Joined: Mon Jul 10, 2000 4:51 am

RE: A Question About Fog And An Apology.

Thu Nov 27, 2003 6:05 am

During WWII, returning British bomber crews had real problems with fog in the early morning. Some airfields had trenches lining the runway, filled with gasoline. These were set ablaze, clearing the fog away. An expensive and crude method, but it worked.
 
Guest

RE: A Question About Fog And An Apology.

Thu Nov 27, 2003 6:23 am

I flew out of SLC for many years. During the winter months when there's a high pressure area over the Wasatch Front. One of the "tricks" that the airline guys use to help each other get out during foggy conditions is to turn their airplanes so as to blow the hot engine exhaust at the RVR sensors. This frequently caused the RVR to improve enough to one or two aircraft out.
 
Mr Spaceman
Topic Author
Posts: 2723
Joined: Thu Mar 15, 2001 5:09 am

RE: A Question About Fog And An Apology.

Thu Nov 27, 2003 6:27 am

Hello Av007.

Thanks for that neat info. The last thing a tired Lancaster bomber crew would need after returning from a mission would be a thick layer of fog covering their airfield. Especially if they were low on fuel or damaged.

I suspect that when those trenches were set ablaze, not only did the heat help to evaporate the fog, but they also acted like runway edge lighting.

I just hope that when those trenches were lit up, they didn't look like this!!!! "Holy Smokes"  Wow! that would sure have freaked out a bomber crew on final.  Laugh out loud


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hehehehe just kidding!

Chris  Smile
 
Guest

RE: A Question About Fog And An Apology.

Thu Nov 27, 2003 6:34 am

Ahh! But just think of the incentive that the Lancaster crews had to keep it on the center line.  Big grin

 
Mr Spaceman
Topic Author
Posts: 2723
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RE: A Question About Fog And An Apology.

Thu Nov 27, 2003 6:55 am

Hello Jetguy.

Your comment about the incentive to keep it on the center line cracked me right up! Big grin You sure wouldn't want your wingtips wandering to close to the runways edge. That's for sure.

Your explanation about the one "trick" that some airline crews would use to magically improve the visual conditions between the RVR sensors was great to learn about. Very sneeky indeed!

A quick question.

What would an average "minimum" RVR measurment be to allow an airline crew to takeoff? I'm sure it varies between aircraft types, type of operation and different company policies. Would a 3000 ft RVR minimum be in the ball park for a A320 for example?

I believe some reasons why RVR distance before departure is so important are that ..... not only does the flight crew need to see the runway that they're screaming down in order to stay on it, but in the case of a runway incursion by another aircraft that's lost in the fog, the pilots need to be able to avoid another fatal accident like what happened at Tenerife when the Pan Am & KLM 747's crashed into each other in the murk!

Chris  Smile
 
aloges
Posts: 14807
Joined: Tue Jan 17, 2006 3:38 am

RE: A Question About Fog And An Apology.

Thu Nov 27, 2003 6:57 am

Chris, Paris CDG had a system called "Turboclair" installed. However, it's now abandoned according to the info on this photo:


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Mr Spaceman
Topic Author
Posts: 2723
Joined: Thu Mar 15, 2001 5:09 am

RE: A Question About Fog And An Apology.

Thu Nov 27, 2003 7:12 am

Hello Aloges.

Thank You very much for posting that photo. I couldn't find it in the database.  Sad

That is one of 3 different photos that I have the ID numbers for writen down somewhere (I can't seem to find them).

I was going to use these 3 pix in a question about how many International Airports around the world are currently using this fog dispersal system or used to.

There are some current websites with info about these systems on the web.

Thanks again,

Chris  Smile
 
ThirtyEcho
Posts: 1411
Joined: Tue Jan 01, 2002 1:21 am

RE: A Question About Fog And An Apology.

Thu Nov 27, 2003 7:40 am

Then there is the "damn the fog" school of operations. During WWII, Curtis LeMay had his bomber crews practice so-called "blind" takeoffs in which there really was no RVR at all. According to my B-24 flying uncle, the aircraft was perfectly aligned on the runway centerline and the pilot set his DG to the "N" heading while the co-pilot maintained the actual heading on his instrument. With full power applied, the pilot concentrated on holding the "N" line exactly while the co-pilot referenced the edge of the runway for excursions. After takeoff, required turns were made with reference to the co-pilot's DG until the pilot reset his.

It must have been hairy beyond words; you are flying an airplane way over max allowable overload with gasoline, ammunition and high explosive bombs. If just one of the four engines malfunctions only slightly, you not only won't make it into the air but you are headed off the side or end of the runway to your doom, even if you maintain heading exactly.
 
411A
Posts: 1788
Joined: Mon Nov 12, 2001 10:34 am

RE: A Question About Fog And An Apology.

Thu Nov 27, 2003 1:06 pm

For those that operated into/out of CDG during the 80's-90's (yours truly included) found that the 'turboclair' indeed worked very well in dispursing fog on the northern runway. However, it was very expensive to operate.

On many occasions in DXB (during the early winter when fog is ever-present), three or four engine widebody aircraft have departed, and in so doing increased the RVR so that twins (737's for example) could depart.
Twins required 400 metres RVR, the TriStar (for example) required only 175 metres.

In fact, ATC arranged widebody departures for exactly this reason
Worked like a charm.

Mr. Spaceman...hope you're feelin' better!

[Edited 2003-11-27 05:09:42]
 
Guest

RE: A Question About Fog And An Apology.

Thu Nov 27, 2003 2:22 pm

I can't answer for the Part 121 or Part 135 guys out there, each company will have their takeoff minimums listed in their ops specs. For Part 91 corporate operations there are no takeoff visibility limitations - we could legally go with zero/zero if we could find the runway and had the 'nads to do it. In practice, we look for around a 1/4 mile vis. We need a little more if the runway doesn't have center line markings and we can get by with a little less if it's got center line lights.

Jetguy
 
cptkrell
Posts: 3186
Joined: Sun Sep 23, 2001 10:50 pm

RE: A Question About Fog And An Apology.

Fri Nov 28, 2003 12:44 am

Jetguy; 'nads, yes, and a VERY important reason to take off in 0/0 (I'm thinking of runway incursions, like a deer), that happened to a friend some years ago. Reminds me of the cartoon where the copilot asks the FO; "Hey, Cap'n, what are all these mountain goats doing up here in the clouds?"
Regards...Jack
 
Guest

RE: A Question About Fog And An Apology.

Fri Nov 28, 2003 3:05 am

Jack...
Haven't you heard about the first rule of instrument flying? "What you can't see can't hurt you..."  Innocent

Actually, you raise a very good point. You must use a lot of judgment when it come to stuff like that. (That's where the 'nads come into play.) The second rule of instrument flying is: "What's safe isn't always legal and what's legal isn't always safe." If you're planning on having a long and prosperous career in this field you need to make sure that your operations are BOTH safe and legal.

Like you mentioned, there are airports where animals can be a real problem. Fortunately, I've never hit anything as big as a deer - I've nailed a pig though!

Jetguy
 
Mr Spaceman
Topic Author
Posts: 2723
Joined: Thu Mar 15, 2001 5:09 am

RE: A Question About Fog And An Apology.

Fri Nov 28, 2003 4:55 am

Hi guys.

Thanks for your replies. Your stories & info are great!  Big thumbs up

> ThirtyEcho, your story about the "damn the fog" school of operations was very much beyond words.For a B-24 Liberator crew to take off "blind" with a high possibility of a very bad outcome is stunning to think about. God Bless your uncle!


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> 411A, it sounds like the controllers at Dubai Airport (DXB) were/are very decent people. It's nice to hear about ATC & pilots working together to arrange for several heavies to depart through the fog first so that smaller jets can get airborne too.

Here's a photo showing what appears to be 5 fog dispersal pads to the right side of the runway's threshold (no longer in use I guess) at Paris's Orly Intl Airport (ORY). This is one of the pix that I told Aloges about.

Ps. Thanks for the kind words. I'm feeling much better now. I have a medical problem that was handed down from my dear father & his dear mother (my Grandmother). I'm on some meds now which are helping a lot. I'll be grounded I guess for quite some time. Oh well, it could be worse!  Smile


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> Jetguy, Thanks for your info. Wow, you hit a pig! What was the damage?

Imagine what you could hit while landing in this fog bank. A Moose perhaps!  Wow!


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Chris  Smile

 
Guest

RE: A Question About Fog And An Apology.

Fri Nov 28, 2003 5:45 am

Chris...
I've mentioned my Pig incident before. About four years ago I was departing Meacham Field in Fort Worth, Texas. It was an evening departure and we were deadheading to Houston to pick up some passengers. A few knots before V1 something darted out in front of us and we hit it. We aborted the takeoff and taxied back to the ramp. The tower controller had someone take a truck out on the runway to see if they could find out what we had struck. They found a 200+ pound ferral pig lying dead right on the runway center line!

We were extremely lucky, an animal that size, If we had hit it dead on, would have easily taken out our nose or main gear. As it was, he was hit by our nosewheel chine and we suffered no other damage.

I spoke with the tower controller and he mentioned that he had to fill out a special form for the FAA. He asked me to wait while he looked for it, but he couldn't find one so he simply took a "Bird Strike Report" and crossed out the word "Bird" and wrote "Pig". I guess that I'm the only person to have ever filed an FAA Pig Strike Report.

Jetguy
 
OPNLguy
Posts: 11191
Joined: Tue Jun 15, 1999 11:29 am

RE: A Question About Fog And An Apology.

Fri Nov 28, 2003 6:16 am

>>>What would an average "minimum" RVR measurment be to allow an airline crew to takeoff?

Generally speaking, airlines here in the USA can takeoff with either a minimum of RVR1600, RVR600, or RVR300, the latter two values requiring multiple transmissometers with all 3 showing that minimum value. Other factors are what equipment the airport has installed, what equipment the airline has installed, and what the authorizations the airline's Ops Specs contains.

 
Mr Spaceman
Topic Author
Posts: 2723
Joined: Thu Mar 15, 2001 5:09 am

RE: A Question About Fog And An Apology.

Fri Nov 28, 2003 7:35 am

Hi guys.

> Jetguy, I'm sorry that I didn't read your story before about your "PIG" strike just before reaching V1. Thank God you and your co-pilot or anyone else were not hurt. I'm sure your impact experience with a 200+ pound ferral pig is quite unique! I agree, you guys were extremely lucky.

Just for the sake of interest, here's a few NTSB reports involving deer strikes. Nobody was injuried.

http://www.ntsb.gov/ntsb/brief.asp?ev_id=20030826x01404&key=1
http://www.ntsb.gov/ntsb/brief.asp?ev_id=20030814x01337&key=1
http://www.ntsb.gov/ntsb/brief.asp?ev_id=20030714x01100&key=1
http://www.ntsb.gov/ntsb/brief.asp?ev_id=20030930x01627&key=1

> OPNLguy, Thank You for your info about the different RVR values that are normal for allowing an airline flight crew to takeoff. I would have never expected an RVR as low as 300 feet to be acceptable. I guess I was way of the mark with my wild guess of 3000 feet. hehehe  Laugh out loud

Chris  Smile

 
OPNLguy
Posts: 11191
Joined: Tue Jun 15, 1999 11:29 am

RE: A Question About Fog And An Apology.

Fri Nov 28, 2003 8:03 am

That RVR 300/300/300 is not very common, and Seattle's 16R, and Salt Lake City's 16R/34L and 16L/34R are the only 5 runway ends I can think of that are authorized at the moment, and the HUD/HGS in the aircraft (and the SMGCS on the ground) make it all possible. Too bad we can't land with RVR 300... It got so foggy at SMF one time a couple of years back that I actually had to divert a Cat-IIIa equipped aircraft sincxe we needed RVR 700 to land and the weather was stuck at RVR 600.

Most major airports in the USA are good down to RVR 600/600/600, usually the runways that are also served by a Cat-II or Cat-III procedure that entails better runway lighting installed than a runway served by only a Cat-I procedure. Those runways only served by/equipped for Cat-I ILS procedures usually have the RVR 1600 (or 1/4 mile) minima.

[Edited 2003-11-28 00:05:19]
 
RNOcommctr
Posts: 779
Joined: Tue Jan 16, 2001 12:26 pm

RE: A Question About Fog And An Apology.

Fri Nov 28, 2003 9:40 am

Here at RNO, we used to have a contract for an aircraft that did "fog-seeding". Our fog comes in the winter and is called "pogonip", an old Indian term for "causing airport problems". (Actually, I have no idea what the word means!) It happens when high pressure builds in after a snow or rain storm, trapping moisture from the precip close to the ground. It can persist for days. I remember that during the Christmas holiday season back in 1987, we lost about 70% of our flights over a seven day period.

The idea behind the fog seeding was that a twin Cessna would drop silver iodide crystals into the fog. I'm not sure of the exact chemistry, but somehow the crystals would attract the moisture in the fog and then the moisture would fall to the ground in odd little snow pellets. The strategy was that if the fog could be made thinner, the sun would break a hole through the fog and once the heat of the sun reached the ground, the fog would burn away.

Nice theory, but in practice, too many conditions had to be exactly right or it wouldn't work. I'd say it helped maybe a third of the time. Many times, as the sun got higher in the sky, the fog would get burned away naturally by noon or so. Plus, the fog seeding was very expensive!
 
OPNLguy
Posts: 11191
Joined: Tue Jun 15, 1999 11:29 am

RE: A Question About Fog And An Apology.

Fri Nov 28, 2003 10:03 am

>>>(Actually, I have no idea what the word means!)

While I think your first definition has merit, a google search turned this up (out of many hits):

Pogonip -- Ice fog (fog consisting of tiny suspended ice crystals). POGONIP is an American Indian word (in the Ohlone language) applied mainly to ice fogs in mountain valleys of the western United States.(12/15/00)

One of our past training guys was a real weather nut, and he posed the "POGONIP" question on our annual dispatcher recurrent test. Drove everyone crazy, and in those pre-internet days, no one could easily figure it out. I called FSS out in SLC, and one of the old-timers there had the answer for me...  Big grin

 
Mr Spaceman
Topic Author
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Joined: Thu Mar 15, 2001 5:09 am

RE: A Question About Fog And An Apology.

Fri Nov 28, 2003 10:24 am

Hi guys.

I'm very Thankful for your replies.

> RNOcommctr, your info about "Fog-Seeding" is very interesting. I've seen TV shows about it's process in the past. Strange but TRUE!

Learning about how guys would take care of business in the aviation industry is a major part of the fun of being a member of this forum.

"POGONIP"....I'll have a dream about it tonight! I hope it won't be scary!> OPNLguy,

> OPNLguy, sometimes I wish I was a weather nut!

Chris  Smile
 
SlamClick
Posts: 9576
Joined: Sun Nov 23, 2003 7:09 am

RE: A Question About Fog And An Apology.

Thu Dec 04, 2003 12:29 pm

A certain well-known west coast airline with smiles on their airplanes was allegedly once invited to stop using their jetblast to clear the RVR transmissometers at SMF. Noise complaints from the few residents west of the airport, apparently. Second or third in line on the parallel taxiway could just turn a few degrees to the right and the RVR would magically come up. Of course I might be making this up.

I have stood on the ramp at RNO during the fog seeding. I can attest to the snow pellets precipping out of the otherwise very stable icefog. It did seem to carve a hole in the "pogonip" just about adequate for one or two arrivals. Problem was that, even with a full ILS, Reno had very high minimums, about 600 and 2 if I remember right. The seeding aircraft had to be based elsewhere.

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