Manipulating RVR

[av8boy]

Saw this http://www.hindustantimes.com/news/181_1882732,000600010001.htm and wondered about how it works where you are.

Briefly, the article, entitled, "How jumbo jets are helping clear the haze at the airport," talks about ATC launching wide-bodies ahead of all others at the Indira Gandhi International Airport during dense fog because "...Each jumbo takeoff leads to an increase of 50 metres in the RVR..."

I've worked at one tower where, on mornings when the RVR was too low for air carrier ops, one particular carrier would request taxi down the entire length of the runway, knowing full well that they could get the RVR to increase to a usable level if they paused near the RVR equipment and blew a little hot air toward them. Of course, given the vis, we couldn't see them doing this so we didn't know it was happening. All we knew is that the RVR increased. :rolleyes:

I'm really not tremendously comfortable with this, given the time-limited nature of the "cure," but obviously it happens. I just don't recall ever seeing it institutionalized as reported in this story. So, thoughts? Where you are is this legal, not legal, done, not done, good idea, bad idea?

Dave

PS (and you know who you are := ) a search for "RVR" here on PPRuNe must be too short, because it comes up empty.

[bookworm]

There are some hazards (http://aviation-safety.net/database/record.php?id=19630904-0&lang=en) associated with attempting to disperse fog this way.

[HEATHROW DIRECTOR]

Only attempted manipulating I came across was one LVP day at Heathrow when a pilot said something like: "Don't give us any more RVRs after we pass 1500ft". Needless to say, I ignored him!

[BurglarsDog]

Ah the old RVR arguement / discussion! Good to revisit!!
In UK I remember sitting in Brawdy tower and watching as the fleet taxied out on a very foggy day. Only a thin layer though (advection fog?) so we could still see SQN tailfin numbers etc. Regardless of what the runway caravan controller reported (unique British idea me thinks) the risk remained with the pilot and he / she departed. I think the ATC RT changed to move the responsibility for a clear runway departure instruction from ATC to the pilot i.e Cleared for take off at your discretion etc.
Over in Oz some years later "Reduced Visibility" operations required a visit by a suitably qualfied ATC0 to the duty threshold from where he/she recorded the number of runway ligts that could be seen. This info was passed to the TWR who cross referenced a table to get the distances, and gave the thumbs up or down to taxiing aircraft. The problem was, with the naked eye, over increased distance the lights tended to merge together, so you couldnt guesstimate an accurate range. But, with binoculars you could distinguish individual lights, or not as the case may be, a lot further up the runway.The rules didnt mention the use of binos and perhapes still dont.
So, were the readings accurate and therefore legal? Didnt seem to make a lot of differene, because the pilots still taxied out, lined up - swore blind they could see the minima - and departed - safely - no cows on the runway in Gippsland!
Still miss those early morning airfield inspections. Best job in the world !!
DogGone :ok:

[throw a dyce]

At Aberdeen in the 80's the Chinooks had a similar effect.It only lasted a short time,and at the 16 touchdown only.I think that they churned so much hot air in the hover that it lifted the RVR slightly.They also were good at snow blowing,cracking tower windows,but had a knack of self destructing.:(

[BurglarsDog]

Chinook over the threshold in Oz - Oh no!! 3 min delay due Wake Turbulence!! Fog would return no doubt.

Go figure - ICAO 4444 / aNNEX2 ??? No standard there!! But I digress.:=

BD

[The Highlander]

All i remember about RVR is going to the RVR twr at brize on freezing cold we foggy mornings and having the living C@@p scared out of me as tristars and vc10s and other biggies made approaches. whilst hoping the approach contollers had him lined up properly.the twr shaking is still a clear memory as the jets passed either on missed approach or successful approaches. was not a nice feeling

[CUNIM]

During the sixties in Aus we taxied a Lockheed Electra up and down to get over the 800 yard visibility, big stirring blades on that machine.:ok:

[LeadSled]

Aaaahh!!!, the good old days.
I am reminded of a "well known" (No !, not "The Corporation") British carrier, in the days of very few RVR direct measurements, and the "rule of thumb" was "six lights", for takeoff.
Three on the right, three on the left, 3+3=6, viz. must be OK, let's go!! Isn't that what "they" meant, the Fleet Manager never complained??
And in Oz., the justly famous case of the "approved observer", the "ramp safety officer", sent out to "count the lights" at the threshold --- nobody told him it was the sequential runway lights down one side that he (no she's in those days, well before PC) was supposed to count, not every light he could see, including VASIS lights, taxiway lights and so on.
Resulting in some rather colourful comments from departing Captains, particularly those who aborted, not limited to allegations of illegitimates tower controllers copulating .
Tootle pip!!

[055166k]

If measures are taken that lead to an improved RVR and aircraft are able to take-off and/or land ...then I say good result. My job is to keep them moving rather than find ways to stop them.
Let's look back a few years:remember FIDO?
Ever hear of pilots asking to follow a 747 down the ILS to fly down the enormous cone of dispersed fog? [at a safe distance of course]
At one airport the morning "rush" was one DC9 which backtracked to clear the fog then took off, followed by four Viscounts which kept it clear until they were all gone.
Not common occurrences I admit.....but worked at the time; I also recognise that modern practice may frown on this, especially with the huge technological advances that have been made in Low Vis procedures.
The ultimate dispersal technique may be "turboclair"....well done the French....a system of jet engines at the runway edge which dispersed fog....and could be turned on and off as required.
I think you would need to justify the comment or suspicion that a pilot would deliberately only clear a transmissometer area rather than the runway, because that is plainly absurd and dangerous.

[Sleeve Wing]

At one airport the morning "rush" was one DC9 which backtracked to clear the fog then took off, followed by four Viscounts which kept it clear until they were all gone.

055166k.
That wouldn't be MME, early eighties, would it ???

[av8boy]

I think you would need to justify the comment or suspicion that a pilot would deliberately only clear a transmissometer area rather than the runway, because that is plainly absurd and dangerous.

Push, push push. Fine then. Saw it. That's why the :rolleyes: was inserted. Also why it didn't seem like such a good idea. Hence the thread.

[Max Angle]

"Don't give us any more RVRs after we pass 1500ft". Needless to say, I ignored him!Doesn't make any difference, once you are inside the OM or equivalent position (4 miles at LHR) you can continue the approach to DH/MDA and land if the required visual reference is obtained regardless of the RVR passed by the tower. Perhaps the pilot in question didn't fully understand the rules and assumed he would have to go-around if the RVR fell below the minimum required.

[eyeinthesky]

Max Angle:

"once you are inside the OM or equivalent position (4 miles at LHR) you can continue the approach to DH/MDA and land if the required visual reference is obtained regardless of the RVR passed by the tower."

Not strictly true. The UK ANO stipulates that an instrument approach may not be continued below 1000ft above aerodrome level if the RVR is less than the minimum required. Once below 1000ft AAL the approach may be continued to MDA(H)/DA(H) as appropriate. 4 DME on a 3 deg GS is approx 1200ft AAL so if the RVR is below minima at 4DME you must go around. That would be the reason for a request not to pass RVR values until below 1000ft AAL.

I'm sure some other will give you the exact ANO words and reference.

[Max Angle]

Not got a recent ANO to hand but 1000ft certainly used to be the rule many moons ago. JAA rules (via the company ops. manual) now state that 1000ft AAL is only used if there is no OM or equivalent position. An non-precision approach using timing with no DME or OM would be an example. As usual JAA complicated matters instead of simplifying them.

[78deg]

JAR OPS applies to JAR OPS approved operators, and the ANO to other UK operators.

[The AvgasDinosaur]

Please excuse my ignorance on this, but does the approach speed have any bearing on acceptable RVR levels. I recall Aer Lingus Carvairs and Cambrian Dakotas appeared to be able to land when all the Caravelles, Comets 1-11s etc were holding at Congleton Honiley and Burtonwood Pole Hill and similar for Ringway as it then was.
Be lucky
David

[javelin]

We use 4 miles/OM when it is published in the sim and on line.