need help with RVR
- Thread starter tailskid
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sopdan
Well-Known Member
captainphil
Well-Known Member
What is RVR and when/where will I learn this?
CaptBill
Well-Known Member
I needed a "RVR for dummies" explanation to help understand this concept, This is the best way to desribe it that I know:
FARs dictate that most domestic airports DO NOT have ceiling minimums; rather, visibility is the controlling factor with respect to weather requirements for dispatch. There are a few exceptions like Jackson Hole, WY where ceiling minimum is specified.
Most airports are equipped with runway visual range (RVR) measuring devices. It is possible to have RVR minimums although the prevailing visibility is below minimums. The logic here is that the machine is more accurate than some controller picking out and seeing something from 1/2 mile away and then calling the vis 1/2 mile.
Typical RVR Vales are:
RVR: 5000 feet = 1 statute mile vis
RVR: 2400 feet = 1/2 statute mile vis
RVR: 1600 feet = 1/4 statute mile vis
* Why is 2400 feet equal to 1/2 mile instead of 2500 feet? Or, 1600 feet equal to 1/4 mile instead of 1250? Perhaps an ATC guy can answer that.
There are usually three transmissometers (machines that measure RVR) located at airports, at least large airports. They are placed at the touchdown area of the runway, the mid point and the end of the runway. They are known as touchdown, mid and rollout. It is quite possible to have quite a spread in visibility from one end of the runway to the other. So the question then becomes: How much visibility do we need to takeoff or land, and what transmissometer (s) is/are needed?
Let's talk about takeoffs first since that was the jest of the question:
Takeoff minimums are listed on the Jeppesen airport pages for each runway. PDX, LAX and IAH all list 600 RVR for takeoff minimums as an example. Takeoff minimums are normally expressed in terms of visibility, without regard for ceiling, except in certain situations where obstruction clearance is a concern. In those cases, specific requirements will be noted on the airport pages.
Standard takeoff minimums for two engine aircraft are one mile vis (RVR 5000). Three and four engine aircraft are 1/2 mile and 2400 RVR. These are broad minimums with no credit for additional visual clues. Minimums usually become 1600 RVR but can be as low as 600. You can get to 1600 RVR with:
1. Operative high intensity runway lights -OR-
2. Operative runway centerline lights -OR-
3. Runway centerline marking.
If none of these things are available, you can still takeoff legally at 1600 RVR provided you have markings or runway lighting that provides you with adequate visual references to continuously identify the takeoff surface and maintain directional control. Pretty broad allowances here that basically says "use your judgement".
You can go to 1200 RVR (1000 in Continental's OpsSpecs)if you have:
1. Operative Runway Centerline lights -AND_
2. You have two (2) operative RVR transmissometers serving the runway to be used. Both systems are controlling meaning that if either reports a RVR below what you need, it over-rides the one that is reporting a higher (and perhaps legal) visibility number. Mid RVR may be substituted for either the touchdown or rollout RVR if either is inoperative.
You can go to 600 RVR (typical takeoff minimums at IAH, PDX and LAX) if you have ALL of the following:
1. Operative Runway Centerline Lights
2. Runway Centerline Markings
3. Operative touchdown AND rollout zone RVR reporting systems serving the runway to be used and BOTH are controlling. If three RVR systems are installed and operative all three are controlling. If one system is inoperative, the takeoff is authorized if the remaining two systems are at or above the appropriate values. Of course the runway posted takeoff minimums may dictate takeoff minimums higher than 600 RVR. Those posted minimums will dictate how low you can go. Continental has exemptions that allow using 500 RVR and other carriers may have something different in their OpsSpecs. I think Alaska has lower minimums as well as they may use their HUD displays as a tool to lower minimums.
So here goes my takeoff minimums thought process:
1. I am good for 1 mile and 5000 RVR in a two engine aircraft.
2. If I have adequate visual references, which 99 percent of the time I do, I can go down to 1600 RVR.
3. If I have Runway Centerline Lights -AND- two RVR transmisometers reporting at or above 1200 RVR, I can reduce my minimums to 1200 RVR.
Continental OpsSpecs allows for 1000 RVR under these circumstances if RVR is reporting at or above 1000.
4. If I have Runway Centerline Markings -AND- Operative Runway Centerline Lights -AND- I have all three transmissometers reporting 600 RVR or greater, or two if one is inoperative, I can takeoff at 600 RVR unless:
The airport has posted higher takeoff minimums for that specific runway or your OpSpecs specifies a higher value. These are generic values and again as a caution, you must review your own carriers OpsSpecs for more restrictive or less restrictive requirements.
You will always want to have a takeoff alternate if takeoff minimums are below landing minimums. That makes sense since you would be unable to return to the takeoff airport if a problem developed.
We can talk about landing minimums another time if anyone is interested.
CaptBill
Well-Known Member
My above post was not written specifically to you as I know as an American Eagle pilot doing 121 ops you already know most of what I wrote. I used your post as an anchor to provide more information than you may have wanted. I agree with you that RVR and the specifics of how to employ it are confusing at times.