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Author Topic: What exactly does RDR mean?  (Read 4020 times)
wpestle
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« on: January 24, 2010, 10:43:23 PM »

In listening to the tower at KORD during snowy days, the controller after giving landing clearance to an a/c always gives the pilots wind heading and strength, info on runway braking conditions, and a number for RDR. Now, I believe that RDR means 'Runway Distance Remaining', but in what way is it meant in this sort of exchange? If the controller says RDR 5000, does that mean that of a, say, 10000 ft runway, only 5000 feet have been plowed and are guaranteed to be passable? That is what I take it to mean, but thought some of the pilots out there might be able to clarify. Thanks!
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Jason
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« Reply #1 on: January 24, 2010, 10:54:00 PM »

RVR or Runway Visual Range which is the visibility measured in feet (in the United States) that a pilot would see in a moving airplane down the runway. A complete RVR consists of 3 separate beams and 6 sensors (Touchdown, Midpoint, and Rollout).

RVR is typically given when visibility is less than 1 statute mile so a pilot has a more exact readout of visibility than expressed in statue miles (ie. 1200 RVR vs. 1800 RVR).
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wpestle
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« Reply #2 on: January 24, 2010, 10:59:26 PM »

Thanks Jason. So does this mean the pilot can expect to visually pick up the runway at 5000ft if the RVR (not RDR, my bad, and thanks for not pointing that out) is 5000?
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Jason
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« Reply #3 on: January 24, 2010, 11:37:25 PM »

Thanks Jason. So does this mean the pilot can expect to visually pick up the runway at 5000ft if the RVR (not RDR, my bad, and thanks for not pointing that out) is 5000?

Usually the answer is yes, but not always since the touchdown RVR is technically measured at the touchdown zone and not prior to it (where the DA/MDA is reached); however, the flight crew must have the prescribed flight visibility for the specific approach they are flying before descending below the DA or MDA.

Here's a good description from the December 1996 issue of IFR Refresher (page 11):
Quote
RVR is defined in FAR Part 1 as, "...runway visual range as measured in the touchdown zone area." The definition doesn't use the word "visibility." RVR is NOT visibility. RVR is the measurement of the distance at which the pilot is likely to be able to see the high intensity runway lights (HIRLs) once the aircraft has touched down on the runway surface in the runway's touchdown zone.
« Last Edit: January 24, 2010, 11:50:07 PM by Jason » Logged
wpestle
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« Reply #4 on: January 24, 2010, 11:41:05 PM »

Gotcha, thanks again!
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Jason
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« Reply #5 on: January 24, 2010, 11:49:29 PM »

Gotcha, thanks again!

Sure thing, see my edited post (above) for more information and another reference.
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jmcmanna
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« Reply #6 on: January 26, 2010, 03:09:40 PM »

Just for clarification, if the touchdown RVR is 5000, you can expect to see 5000' ahead of you from the beginning of the runway.  It doesn't have anything to do with the altitude the airplane is at.  If the visibility is less than a mile, and an RVR is available, controllers are obligated to issue that RVR to the pilot with a takeoff or landing clearance.
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Unbeliever
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« Reply #7 on: January 26, 2010, 07:44:16 PM »

Usually the answer is yes, but not always since the touchdown RVR is technically measured at the touchdown zone and not prior to it (where the DA/MDA is reached); however, the flight crew must have the prescribed flight visibility for the specific approach they are flying before descending below the DA or MDA.


Flight visibility does trump reported visibility UNLESS it is reported as RVR, then RVR is controlling.  Ref, AC97-1A, and Part 97.

--Carlos V.
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