121 alternates question


Well-Known Member
I've got an interview coming up with a regional (Horizon) in a few days, and I'm trying to make sure I've got the rules for IFR alternates under part 121 figured out.

As I understand it, a departure alternate is required if the WX at the departure airport is below the landing minimums in the OpSpecs. The alternate must be within one hour single engine flying time of the departure airport, and the weather there must meet the requirements of the Opspecs.

A destination alternate is required if the WX at the destination is forecast to be below the minimums listed in the OpSpecs.

For the purposes of an interview (since I doubt Horizon expects interview candidates to know their Opspecs), I was assuming that a departure alternate would be required if the departure WX was below the lowest approach minimums, and the 1-2-3 rule would be acceptable to determine whether a destination alternate was required.

Aside from Opspecs, what would determine the takeoff minimums for a given airport? I'd assume that the Jepp 10-9 would list takeoff minimums, but I'm not sure which would apply if those two don't agree.

Am I understanding the alternate requirements here correctly, and is it reasonable to use the lowest approach minimums and 1-2-3 rule for the purposes of an interview?
If this is your first 121 job I would stick with what you just posted. If it's not, then I guess I would go into it. If you want to discuss derived minimums and how you get those numbers I'll be happy to explain. I think you are on the right track right now and that should suffice. Maybe some of the current Horizon guys, @SurferLucas @pete2800, might be able to shed a bit of light.
If reported departure WX is below landing mins or if any other operational conditions exist at the departure airport that would preclude a return back to that airport, a takeoff alternate is required.

A destination alternate is not required if:
- An approved instrument approach procedure is available at the destination.
- For atleast 1 hour before/after the ETA at the destination airport, the appropriate weather reports or forecasts, or any combination of them, indicate that: The ceiling will be atleast 2,000ft above airport elevation and visibility will be atleast 3 statue miles

That's what you need to know right there, go with that and you'll be fine.

Let's us know how it goes! :)...and good luck
Thanks for the replies! This is my first 121 interview, so I'll just stick with the 1-2-3 rule.

If a takeoff alternate is required, what are the minimums there? Is it the standard 600-2 or 800-2, or is is just the lowest minimums on an approach at the alternate?
I tried to start spitting out part 121 regs during my interview, and I was told rather quickly to stick to 91 for the purposes of answering their questions. SurferLucas nailed it for you.
^^^^THIS! In an interview you are expected to know what you are supposed to know. If this is your first 121 gig, you are not expected to know 121 regs, so don't wrap yourself around the pole on trying to figure it out. Have a command of 91 rules (and 141 or 135 if you work at one of those type operations), and you'll be fine.

In my interview a few years back, when they asked me to finger fly an approach, I straight up told them that I wasn't very familiar with Jepps, as I used NACO/NOS charts for flight instructing, and had only looked at Jepps to prepare for the interview. They understood and cut me some slack...

BTW, a good basic interview question I've heard of few guys failing an interview on at my place is, "what do you need to descend below MDA/DA on an approach." Should be basic knowledge, but people seem to flub it every now and again for whatever reason.