121 Takeoff Wx requirements question

[bgaviator]

Can someone help me verify how I'm understanding the Part 121 takeoff weather requirements?
So unless the company SOP states certain takeoff weather requirements for a given airport, you use the takeoff wx. requirements listed for that airport in the plates?
And if the airport doesn't have specific takeoff wx. requirments that's when you use the 800-2, 900 1 1/2, or 1000-1?
What about just using the general rule for aircraft with 2 engines, or more than 2 engines....I think that's in the general IFR rules...do those not apply when dealing with 121 operations? I think it's where if you have 2 engines you have to have 1 mile, but if it's 3 or more you can have 1/2 mile. I'm so confused with all the different regs depending on the type of operation.

 

[Doc Holiday]

121.651(a) says that you cannot take off when the weather is reported below what is specified in the operators ops specs. If the ops specs do not specify minimums for a particular airport, you are referred to Part 91 and Part 97. 91.175(f) is where the 2 engine 1 sm/3 engine .5 sm rule is found. These values are to be used if no minimum is established by 97.20 (pertains to takeoff mins found in the DP/ODP)

To help break this down, there are two commonly used terms - "standard" and "lower than standard" takeoff minimums. "Standard" takeoff minimums refer to the 91.175 rule regarding 2 and 3+ engine aircraft. "Lower than standard" takeoff minimums refer to relief provided by a company's Ops Specs.

Company issued Jepps (plates) have takeoff mins published in them that show lower than standard takeoff minimums for each particular runway based on the visual aids available. These values are only valid if the company's ops specs provide for lower than standard takeoff minimums AND the DP or ODP allows for standard takeoff minimums.

For example, if a DP says 1 1/2 sm visibility is required, these lower than standard takeoff mins CANNOT be used. If the DP does not specify takeoff minimums or if a phrase such as "...or standard with a climb of 340 feet per NM" is used, you can use lower than standard takeoff minimums. (assuming the aircraft can meet the increased climb gradient if one is specified)

Everything said up to this point is for airports listed in a company's ops specs.



121.637(a)4(i) is where you find the 800-2, 900-1 1/2, 1000-1 values. The first sentence of this reg specifies that 121.637 only applies to airports that are NOT listed in the ops specs. The reg also says that the previously mentioned values only apply if Part 97 (DPs/ODPs) does not specify weather minimums.

Hope this helps.

 

[bgaviator]

it almost sounds like the 1 mile for 2 engine, and 1/2 for 3 or more engine rule doesn't even really apply to 121 operations cause you would think that a 121 carrier would have ops specs for every airport it uses....and even if it happens to divert to an airport not in the ops specs, that's when you applay the 800-2, 900 1 1/2, or 1000-1....correct? So is the 1 mile for 2 engings, and 1/2 mile for 3 or more really just applying to general aircraft flying IFR?
It's still confusing.

 

[Andy Neill]

Here is the decision tree that I used for takeoff minimums.

Is there a HIGHER than standard takeoff minimum published that I cannot get around with a climb gradient etc.? If there is, then I must have at least that ceiling and visibility to takeoff on that runway.

If there is not a higher than standard takeoff minimum published, then I can takeoff if I have at least 1 mile (or 5000 RVR when available).

If I don't have a mile vis (or 5000 RVR when available), do I have at least 1/4 vis (or 1600 RVR in the touchdown zone) AND at least one of the following [centerline lights, runway centerline markings, high intensity runway lights, or anything else that would qualify at adequate visual reference]? If the touchdown zone RVR is not available, I can substitute midfield RVR.

If I don't have that, do I have at least 1000 RVR in the touchdown zone AND the rollout AND centerline lights? Midfield can be substituted for either of the other ends if unavailable.

If I don't have that, do I have at least 600 RVR in the touchdown zone, midfield AND rollout with both RCLM and CL? Any one of the RVRs may be unavailable.

If I don't have that, I can't go. I need to satisy only ONE of the rules to go - I don't have to satisfy all.

Numbers may be different for your company's specific OPSPECS.

 

[Doc Holiday]

it almost sounds like the 1 mile for 2 engine, and 1/2 for 3 or more engine rule doesn't even really apply to 121 operations cause you would think that a 121 carrier would have ops specs for every airport it uses....and even if it happens to divert to an airport not in the ops specs, that's when you applay the 800-2, 900 1 1/2, or 1000-1....correct? So is the 1 mile for 2 engings, and 1/2 mile for 3 or more really just applying to general aircraft flying IFR?
It's still confusing.

It may help you to look up the regs I referenced previously. 91.175(f) specifically says the "standard" takeoff mins of 1 sm for 2 engines applies to operations under 121, 125, 129, and 135 if Part 97 does NOT specify takeoff minimums for that airport. For other operations (i.e. Part 91) you can legally takeoff when the weather is below that specified by Part 97, although it may not be the safest thing to do.

Now if you take a look at 121.651(a), that is the paragraph that refers you to Part 91 and 97 if the company's ops specs do not provide for lower than standard takeoff minimums.

You are now correct on the 800-2, 900-1 1/2,....deal. But that is only if Part 97 does not specify takeoff minimums for that airport.

Remember that Part 97 is what makes the weather minimums found in Departure Procedures (DPs) and Obstacle Departure Procedures (ODPs) a legal value.

I assume you are in training for a 121 carrier if you are devling into this stuff. To get the full picture you need to read these regs and read your company's ops specs. Only when you know what these documents say and put them together will you start to get a true understanding of how they are applied.

 

[twighead]

Wow you guys are making this way more complicated than necessary.

The company Op Specs simply tells you the minimum RVR in which the pilots are trained to takeoff. We can never takeoff with anythng less even if the RVR published on the chart is lower.

Also, if the published minimums (eg. the ones on the jepp chart) are higher than the minimums in the Ops specs, then those published mins (on the chart) are controlling.

Example: Our company take off min (ops specs) is 400 RVR. If the published min for the airport is 500 RVR, then you must have at least 500 RVR to takeoff. Conversley, if the chart says 300 RVR, we still must have at least 400 RVR to takeoff because that is what is in the ops specs.