takeoff mins

[bluelake]

This is a situational question:

Your 135 OpSpec lets you depart with landing mins, say in this case 1/2 mile.

Tower ATIS is calling 1/4, AWOS is bouncing between 1/4 and 3/4. You are at the runup area at the end of the runway and you can consistently see all the way to the end of a 7,000' runway.

I am only asking this because it seems to pop up in conversation in our winter flying, typically associated with fog.


What CAN you do (note I did not say "would" or should")?

More than opinion, I appreciate references to the FARS, AIM, OpSpec's, etc...

Oh yeah, and while I am at it, does anyone know at what point in viz is it called fog versus being called MIST?? I have been wondering that.

Thanks all.

 

[cimepilot]

Well, hopefully there is some RVR at the field that will allow you to takeoff, so ask tower for an RVR reading. If not, ask tower for an ASOS reading and when it says 1/2 mile do not ask again and put the petal to the metal. Other than that, I guess you are grounded.

 

[Mr_Creepy]

Most 135 operators have a "paragraph c" in the ops specs page on take off mins which allows them to depart when weather is at or above landing mins for that runway.

Problem is, the order of the "food chain" for visibility is RVR, Tower, in-flight (for take off only - it's reversed for landing.)

So you have no RVR and tower is saying 1/4. You can't depart until the tower says 1/2. I'd be "petitioning the tower" with your pirep - "Tower I can see the other end of the runway from here."

They may change their visibility.

 

[bluelake]

John,
What you refer to as the "food chain" is exactly my question. Where is this food chain written. BOTH Tower and ASOS are 'offical' sources of weather.

I myself would always defer to the tower's observations, because the tower controls the field.

 

[Mr_Creepy]

[ QUOTE ]
John,
What you refer to as the "food chain" is exactly my question. Where is this food chain written. BOTH Tower and ASOS are 'offical' sources of weather.

I myself would always defer to the tower's observations, because the tower controls the field.

[/ QUOTE ]

I'll do some digging and see what I can find. I've always been told RVR is controlling for departures but it must be written somewhere.

91.175 spells it out for approaches and landings. "Reported visibility" to initiate the approach and "flight visibility" to land.

 

[EatSleepFly]

[ QUOTE ]
I've always been told RVR is controlling for departures but it must be written somewhere.

[/ QUOTE ]

The Ops. Specs. or FOM, is one place. Probably somewhere in the FAR's too.

 

[cimepilot]

I thought RVR was controlling for both takeoff and landing. That's what our ops specs say anyways.

 

[EatSleepFly]

[ QUOTE ]
I thought RVR was controlling for both takeoff and landing. That's what our ops specs say anyways.

[/ QUOTE ]

Yeah, it is. There is nothing in the FAR's that specifies whether RVR or vis. is controlling. Its spelled out in AC 97-1A. If the runway has RVR measuring capability, of course.

Here's the pertinent part:

c. Visibility Measurements.

Visibility measurements at airports are presently reported in terms of statute miles or fractions thereof and, in case of RVR, in terms of feet. RVR equipment is not capable in all cases of reporting the precise increment of feet equal to the usually reported fractions of a statute mile. RVR reports, when given for a particular runway, are controlling for all takeoffs and landings on, and approaches to, the runway.

AC 97-1A- (Everything you need to know about RVR) can be viewed here.

 

[Mr_Creepy]

There it is! Thanks ESF - that's what I was looking for.

 

[SnowHo]

I could be totally wrong but I think BR is 5/8-3/8sm and FG is 3/8sm and below. I dont know what your ops specs say but we can depart with landing mins and above of the approach in use. (which is going to usually be a 1/2) Then we can go down to 1600 RVR with one of a list of stuff. (centerline lights, other stuff i'd have to look at the book) After that we can go down to a 1000 RVR with three things. Then down to 600 RVR with 5 things and three RVR transmitter deallyo's. I thought our specs were pretty standard for every 135 operator but i guess not.