Fuel Requirements for Flight in Ifr Conditions

Section 91.167 sets fuel requirements for IFR operations. It is materially different from the VFR fuel rule in § 91.151 — IFR fuel requires reaching the first airport of intended landing, then flying to the alternate (if required), then 45 minutes of normal cruise fuel.

Paragraph (a) — Basic IFR fuel requirements: No person may operate a civil aircraft in IFR conditions unless they carry enough fuel (considering weather reports and forecasts and weather conditions) to:

• Complete the flight to the first airport of intended landing
• Fly from that airport to the alternate airport (if one is required by § 91.169)
• Fly for 45 MINUTES thereafter at normal cruise speed (the IFR reserve)

Paragraph (b) — When an alternate is required: See § 91.169. Basically: if weather at the destination from 1 hour before to 1 hour after ETA is below 2,000 ceiling AND 3 SM visibility, an alternate is required. The 'flying minimum' that triggers the alternate requirement is the '1-2-3 rule' (1 hour before/after, 2,000 ceiling, 3 SM visibility).

The 45-minute IFR reserve: The IFR reserve is 45 minutes for ALL flights regardless of day/night. It is at NORMAL CRUISE speed and fuel burn — not best-economy or maximum-endurance. This is the floor; many IFR operators carry significantly more.

Paragraph (c) — Mountainous terrain: When operating IFR in mountainous terrain (designated areas), the alternate selection rules in § 91.169(c) apply — specifying that the alternate must be reachable while staying at or above MEA.

The 'IFR reserve at normal cruise' interpretation: The FAA Chief Counsel has affirmed that 'normal cruise' means the speed/burn the aircraft was actually being operated at — not the highest fuel-burn power setting in the AFM. A Cessna 182 operating LOP at 12 GPH calculates its reserve at 12 GPH, not at the 13.5 GPH ROP figure.

Reference: FAA-H-8083-16 (Instrument Procedures Handbook) Chapter 1; AIM 5-1-7 on Flight Planning.

IFR Fuel Reality — § 91.167

The reg is short, but pilots conflate it with § 91.169 constantly. Here's the clean read: § 91.167 tells you what fuel to carry. § 91.169 tells you when an alternate must be filed. Two different questions, one fuel tank.

Paragraph (a) is the baseline. You must carry enough fuel — considering weather reports and forecasts — to (1) fly to the first airport of intended landing, (2) then fly from that airport to the alternate, and (3) then fly for 45 minutes at normal cruising speed (30 minutes for helicopters). That's the legal floor for any IFR flight. Not 45 minutes at hold speed. Not 45 minutes at max-endurance. Normal cruise — the burn you actually plan the trip on.

Paragraph (b) is the carve-out, and this is where pilots get tangled. The fuel-to-alternate requirement in (a)(2) doesn't apply if two things are true: Part 97 prescribes a standard instrument approach to the destination, AND the forecast weather supports skipping the alternate. The specific ceiling-and-visibility thresholds that trigger this — the "1-2-3 rule" most pilots can quote in their sleep — actually live in § 91.169, not here. § 91.167(b) just says "appropriate weather reports indicate" the conditions; § 91.169 fills in the numbers (for one hour before through one hour after ETA: ceiling at least 2,000 ft and visibility at least 3 SM).

So the workflow is: § 91.169 tells you whether you must file an alternate. § 91.167 tells you how much fuel that decision costs. Read them as a pair or you'll confuse yourself on a checkride.

What an Examiner Asks About § 91.167

This reg shows up on every instrument and commercial checkride, and most CFI-Instrument rides. The examiner isn't checking that you can recite (a)(1)(2)(3) — they're checking whether you can plan a real IFR flight without running yourself out of fuel over a layer.

Expect these:

• "What's the IFR fuel requirement?" — Destination + alternate (if required) + 45 minutes at normal cruise. Say it that cleanly.
• "When is no alternate required?" — When the destination has a published instrument approach AND the forecast meets the 1-2-3 thresholds. Name the cross-reference: that's in § 91.169, not § 91.167.
• "If you carry fuel to destination plus 45 minutes only, are you legal IFR?" — Only if no alternate is required under § 91.169. Otherwise no.
• "What's the difference between § 91.167 and § 91.169?" — One is fuel to carry; the other is alternate planning rules. Examiners love this question because most applicants smear the two together.

The trick examiners run: "Forty-five minutes at what speed?" Applicants often say "hold speed" because they're thinking about holding patterns. Wrong. It's normal cruising speed — the planning burn for the airplane you're flying. Get that one right and you've separated yourself from half the room.

Computing IFR Fuel for a Real Trip, Under § 91.167

You're flying a 172 from KAPA to KGCC — about 300 nm IFR. The forecast at your ETA reads OVC020 1.5SM. That's below the 1-2-3 thresholds (ceiling under 2,000, vis under 3), so § 91.169 requires you to file an alternate. § 91.167 now wants you to carry fuel for three legs instead of two.

Run the math at a planning burn of 8.5 gph:

• KAPA → KGCC (destination): ~2.5 hours = 21.3 gal
• KGCC → KCPR (filed alternate, ~115 nm): ~1.0 hour = 8.5 gal
• 45-min reserve at normal cruise: 0.75 hour = 6.4 gal
• Legal minimum: ~36.2 gal on board at takeoff

A 172 with long-range tanks holds about 53 gal usable. You're legal, but the alternate just ate about 8.5 gallons that wasn't on your VFR planning sheet. On a marginal day with headwinds, that's the difference between "comfortable" and "diverting." This is where competent IFR pilots add a personal reserve on top of the legal one — not because § 91.167 demands it, but because the reg is a floor, not a target.

The reg pulls you to a number. What competent adds: a real fuel margin for the weather you actually expect to fly through.