§ 91.169 IFR flight plan: Information required.

Section 91.169 governs the IFR flight plan — what to file, what's required, and when an alternate must be filed. It is the rule that creates the famous '1-2-3' alternate requirement.

Paragraph (a) — Information required: Every IFR flight plan must include the standard ICAO-format information (aircraft ID, type, equipment suffix, departure, route, destination, alternate if required, fuel on board, persons on board, etc.).

Paragraph (c) — The 1-2-3 alternate rule: No alternate is required if for at least 1 HOUR before to 1 HOUR after the ETA at the destination, the weather reports/forecasts indicate the ceiling will be at least 2,000 feet above the airport elevation AND the visibility will be at least 3 statute miles.

Otherwise, an alternate IS required. The alternate selection must meet the standard alternate minima OR the published non-standard alternate minima (NA, or specific values published on the approach chart).

Standard alternate minima:

• Precision approach (ILS or PAR): 600-2 (600-foot ceiling, 2 SM visibility)
• Non-precision approach (VOR, LOC, RNAV LNAV): 800-2
• No instrument approach: VFR conditions from the MEA

Paragraph (d) — IFR over Mountain ranges and on certain routes: Special alternate requirements apply for designated mountainous areas — the alternate must provide for the ability to maintain MEA en route.

The 'NA' (Not Authorized) approach: Some approaches have 'NA' for alternate use, meaning the approach cannot be used to qualify the airport as an alternate (even if otherwise meeting standard minima). Pilots must check the alternate planning notes on the approach chart.

Reference: AIM 5-1-7; FAA-H-8083-16 Chapter 2.

The 1-2-3 Rule — When an Alternate Is Required, Decoded

Every instrument pilot learns "1-2-3" on day one. Then they spend the next 200 hours getting it slightly wrong. The mnemonic is real — it's baked into § 91.169(b) — but the pieces around it trip people up. Let's decode it honestly.

The rule, plainly: you do not have to file an alternate if, from 1 hour before to 1 hour after your ETA, the destination forecast shows a ceiling of at least 2,000 feet above airport elevation and visibility of at least 3 statute miles. Miss any one of those — by a foot, a mile, or a minute — and you're filing an alternate.

• The "1" — the window is one hour before through one hour after ETA, not just at ETA. Two hours of forecast, not a snapshot.
• The "2" — 2,000 feet above airport elevation, not MSL. A TAF reporting ceiling at 3,000 MSL at a 1,500-foot airport gives you 1,500 AGL — alternate required.
• The "3" — 3 statute miles visibility. Statute, not nautical.

Now, if 1-2-3 fails and you are filing an alternate, § 91.169(c) tells you what weather the alternate itself has to show at your ETA there — the "standard alternate minimums":

One more piece nobody talks about until it bites them: "NA" in the alternate minimums box on the approach plate. Some approaches can't be used to qualify a field as your alternate — typically because the procedure isn't monitored, the weather reporting isn't there, or required equipment is out of service. If every published approach at a candidate alternate shows "A NA," that field is off the table. Read the plate before you file.

And don't confuse this reg with § 91.167. § 91.169 tells you when to file an alternate. § 91.167 tells you what fuel to carry once you do. Two regs, one trip — both have to be satisfied.

What an Examiner Asks About § 91.169

This reg shows up on every instrument checkride and again on the CFI-I. Examiners aren't hunting for the mnemonic — they want to see you operationalize it in front of them, with today's TAFs.

• "When are you required to file an alternate?" Don't lead with "1-2-3." Lead with the question the reg actually asks: does the destination forecast guarantee 2,000 and 3 from one hour before through one hour after ETA? If not, you're filing.
• "Walk me through the 1-2-3 rule." One hour before through one hour after ETA. 2,000-foot ceiling above airport elevation. 3 statute miles visibility. Say "above airport elevation" out loud — that's the piece students miss.
• "Once you've filed an alternate, what minimums apply at the alternate?" Standard alternate minimums per § 91.169(c): 600 and 2 for precision, 800 and 2 for non-precision, basic VFR if no approach. Add: "Unless the plate publishes non-standard minimums — then I use those."
• "What does 'A NA' mean on the approach plate?" Alternate Not Authorized. That approach can't be used to qualify the field as my alternate. If every approach at the field shows NA, the field is off my list.

The trick examiners love: the window. Pilots quote "2,000 and 3 at ETA." It's 2,000 and 3 for two solid hours — one hour before through one hour after. A TAF that dips to 1,500 broken thirty minutes before your ETA blows the rule, even if it's severe-clear at touchdown.

Filing an Alternate for a Real IFR Trip, Under § 91.169

You're flying IFR to a destination forecasting 1,500 OVC 3SM at your ETA in a Cessna 172 with a panel-mount IFR GPS and an instrument rating. Walk it through:

Step 1 — Run the 1-2-3 check. Ceiling is 1,500 above airport elevation — below the 2,000 threshold. Visibility makes it (3 SM), but you need both. The rule fails. Alternate required.

Step 2 — Pick a candidate alternate with a published approach. Look at fields within reasonable fuel range with weather forecast to be better than yours at your alternate ETA. Pull the plates. Confirm none of the approaches show "A NA" in the alternate-minimums box. If the field has an ILS, you can use the precision row of the alternate-minimums table.

Step 3 — Apply alternate minimums per § 91.169(c). ILS available, so the alternate's forecast at your alternate ETA must show at least 600-foot ceiling and 2 SM visibility. (These are filing minimums, not approach minimums — once you actually fly to the alternate, you shoot the approach to the plate's published mins.)

Step 4 — Compute fuel under § 91.167. Enough to fly to the destination, then to the alternate, then 45 minutes at normal cruise. Three buckets. Most pilots miss the alternate leg in the math.

The reg is the framework. Your job as PIC is to file an alternate you'd actually want to fly to — not the closest dot on the chart. Weather should be solidly better than the destination, the approach should be one you're proficient on, and the fuel should leave you options when you arrive.