For my company, the following requires the specification of an alternate

1st Alternate:
123 Rule
Landing Performance
Offline Charter
No Instrument Approach Procedure
Driftdown
Mountainous Airports w/high MDAs (Optional)
PIC Discretion (x-wind at or beyond limits, etc)
Takeoff Alternate (departure wx below landing mins)

2nd Alternate:
Marginal (within 100+1/2 of actual + derived minimums) weather at Destination AND 1st Alternate
Use of Exemption 3585 (relief from conditional remarks in TAF, i.e, "TEMPO")

 

Forgive my ignorance... explain "driftdown" anyone?

 

FAR 121.191
Cruising along at FL250 DEN-SLC over the Rockies and engine dies. Said Rocky Mountains are 14,000ish MSL. Our aircraft can only hold 13,000 MSL single-engine at today's weight. You must prove that you're not going to hit a mountain as you "driftdown" from your cruise altitude to your eventual level-off altitude. One has to clear terrain by 2000 AGL on the way down, and arrive over the landing airport 1500 AGL. The plan that is developed and included on our releases assumes that you'll turn around and go back to DEN if the failure occurs prior to the halfway point of the journey. Similarly, you'd continue to SLC if the failure occurs beyond the halfway point. If a failure was to occur in the middle portion of the route and in planning it was found you couldn't make either the destination or arrival cities without hitting a mountain, another city (or two or three) would be specified as your escape plan, a "driftdown alternate."

Alternatively the regs offer a less complex option: Maintain an "enroute net climb gradient" (i.e., maintain level flight or better) on one engine that keeps you 1000 above all terrain, period. This however, requires a lighter weight in the example above. We'd have to bump X number of people off until we could hold 15,000 on one engine.

 

interesting.. thanks for the explanation

 

Very good point. I was riding the jumpseat on a 737 that had to divert due to destination weather. Our original alternate was fine to land at but would not have allowed us to take off with the very full load we had. Long story short, the decision was made to divert to a different airport that would not have required the crew to leave payload behind.

 

Unfortunately, this common sense thinking is not that prevalent. Knowing what is in the book is important, but knowing what works is more important. Just proves that old adage: Just because you can, doesn't mean you should.

 

Hold on here a minute, by that comment I would have figured this was flightinfo.com. I asked the question regarding 121 alternates in a REGIONAL forum because I assumed most REGIONAL pilots are 121 no? Plus there was already a thread on the general topic. If you don't have anything helpful to add, please don't respond.

KiloAlpha & others, thank you for your responses. I am getting technical on the question because of an upcoming interview, and I figure it's better to over prepare than under prepare. KA, one more thing though. I noticed in your response you said that 121 can sometimes be more restrictive than 91. In my example, if you follow the ops specs, 121 actually helped you out because all you needed at RIC to file it as an alternate was 400-1 instead of 600-2, which is posted on the 10-9 page. So just to clarify, can I legally overide the airport's posted "weather minimums to file as an alternate" with the ops specs?

Thanks for the help.

 

This exemption authorizes AA to deviate from 121.169 by reducing the destination weather requirements for listing an alternate to at least 1000 foot ceilings and at least 2 statue miles of visibility.

This exemption includes a number of restrictions to be specified in Flight Manual Part I. A summary of the restrictions is listed below:
- Only operations in the 48 contiguous United States.
- Destination airport must have a Cat II or Cat III approach available for the expected runway.
- The crew must be qualified for a Cat II approach (or Cat III if Cat II is not available)
- Thunderstorms are not forecasted.
- Must be noted on the Flight Plan/Release. It will appear in the fuel block at the bottom of the flight plan.

 

To answer your question in short, yes. That is the purpose of the 121 op specs. They allow you to sometimes take off and land when a part 91 flight would not be able to.

STR8NLVL

 

Thanks for the replies guys. You've been very helpful.