Alternate requirements and fuel planning

Test the destination exception completely

For an ordinary airplane IFR flight plan, §91.169 requires an alternate unless its exception applies. The first airport of intended landing must have a Part 97 standard instrument approach, or an applicable special procedure issued to the operator. Appropriate reports/forecasts, or a combination, must indicate a ceiling at least 2,000 feet above airport elevation and visibility at least 3 statute miles for at least 1 hour before through 1 hour after the destination ETA.

The familiar “1-2-3” phrase omits the approach condition and can hide the whole time window. Do not use only the exact ETA forecast or compare 2,000 feet with MSL altitude. If no qualifying destination approach exists, favorable weather alone does not meet this exception. If the relevant weather is missing or adverse in the window, do not invent a favorable forecast to omit the alternate.

Fictional example: destination ETA is 1800Z. Forecast 2,500-foot ceiling and 4 SM from 1700–1900Z meets the weather portion. A temporary 1,500-foot ceiling at 1730Z means the displayed forecast evidence no longer supports the full exception. Evaluate forecast groups as conditions that may affect the flight, not values to average together.

Even when no alternate is legally required, a prudent plan considers runway/approach outages, terrain, fuel availability, deteriorating weather and reachable diversion airports. The exception sets a filing/fuel minimum; it does not promise a landing.

§91.169(a)–(b): alternate requirement and destination approach/weather exception · §91.167(b): corresponding fuel-to-alternate exception

Apply the candidate’s actual alternate criteria

When an alternate is required, §91.169(c) evaluates appropriate weather at the ETA at the alternate. This is a different time and a different weather test from the destination's ±1-hour exception. Determine a credible alternate arrival after the destination attempt/diversion, not merely the destination ETA copied into another box.

For an airport with a qualifying instrument approach, use the alternate minima specified for the applicable procedure. If none are specified, the airplane standards are 600-foot ceiling/2 SM for a precision procedure or 800-foot ceiling/2 SM for a nonprecision procedure. Those numbers are alternate-planning criteria, not the landing DA/MDA/visibility for every approach.

An A in a triangle on an FAA approach chart directs the pilot to the IFR Alternate Minimums section of the TPP for nonstandard criteria. Read the actual approach, category, runway, weather-reporting, facility and other notes. A NA makes the indicated procedure unavailable for alternate planning under its stated conditions; assess whether another applicable procedure is usable rather than automatically declaring every procedure at the airport equivalent.

If no qualifying instrument approach is published or applicable special procedure exists, §91.169(c)(2) requires forecast ceiling/visibility allowing descent from the MEA, approach and landing under basic VFR. “800-2 for every airport” is wrong. Terrain, airspace and actual VFR requirements must permit that operation.

Check aircraft equipment/approval, procedure availability, NOTAMs, weather reporting, runway suitability, hours and services. A forecast above alternate minima does not restore an inoperative required aid or closed runway. Select an airport that remains usable when the likely destination problem occurs, including the missed approach and onward diversion.

§91.169(c): procedure-specific, standard and no-approach alternate minima · IFH Chapter 1, 1-16 and 1-27: alternate-minimum chart symbols and TPP lookup · FAA current TPP and Chart Supplement products

Use the planning rule for the installed GPS approval

Basic GPS and GPS/WAAS approvals have different planning provisions. Check the actual receiver approval, flight-manual supplement, current navigation database, required integrity prediction and NOTAMs. A portable or VFR GPS does not supply IFR approach capability.

Under current AIM 1-1-17, qualifying TSO-C129/C196 users with fault detection and exclusion (FDE), the required preflight RAIM approach-integrity prediction, knowledge/training/approval may plan a GPS-based IAP at either the destination or the alternate, but not both. The alternate planning lines are limited as stated in the AIM. If those conditions cannot be met, the required alternate needs an anticipated available non-GPS procedure that the airplane can fly. Basic GPS also retains its applicable non-GPS route-equipment/infrastructure requirements.

Under AIM 1-1-18, approach-approved WAAS can support GPS-based planning at both locations within its applicable provisions. For the ordinary WAAS alternate case, base planning on the LNAV or circling line and the Part 91 nonprecision alternate-weather criteria, including nonstandard notes. Do not use an LPV DA as if it established “600-2” alternate planning. Upon arrival, displayed available LPV or LNAV/VNAV service may permit flying that authorized line. Planning and actual available approach service are separate decisions.

The AIM includes specific approved baro-VNAV/RNP exceptions for properly trained/authorized users; do not assume they apply to every WAAS installation. Some approaches remain alternate-NA for reasons such as weather reporting. A WAAS outage, interference NOTAM or receiver failure can change the planned options; evaluate those contingencies and the actual capability before launch.

AIM 1-1-17(b)(3)–(4) and 1-1-18(c)(9): basic GPS and WAAS alternate planning restrictions · AIM 1-1-18(c)(5)–(8): WAAS NOTAMs, service and outage implications

Calculate the regulatory fuel in flight phases

For an airplane in IFR conditions, §91.167 requires enough fuel, considering weather reports/forecasts and weather conditions, to reach the first airport of intended landing, fly from there to the alternate unless the rule's exception applies, then fly 45 minutes at normal cruising speed. For this course, use the airplane requirement; helicopter provisions differ.

The exception to the alternate leg has the same qualifying destination-approach and ±1-hour 2,000-foot/3-SM conditions as the ordinary filing exception. It removes the required alternate leg, not the 45-minute reserve. Other operational needs and a prudent diversion option still matter. Filing an alternate voluntarily or naming one in an app is not a substitute for applying the actual fuel rule to the mission.

Use usable fuel and actual aircraft performance data. Plan start/taxi, climb, cruise, descent/approach, missed-approach/diversion exposure and reserve consistently, without double counting overlapping segments. Account for power, mixture, altitude, temperature, wind and equipment operation using the real AFM/POH. A fuel total from a generic airplane profile is not evidence for this installation.

Fictional arithmetic: usable fuel for the destination segment is 18 gallons, the required alternate segment 6 gallons, and normal cruise consumption is 10 gallons/hour. The 45-minute reserve is 7.5 gallons, so those stated airborne components total 31.5 gallons. Add any start/taxi or other consumption not already included before evaluating departure fuel. These are study inputs, not an aircraft performance recommendation.

§91.167(a)–(b): destination, alternate, normal-cruise reserve and exception · §91.103(a): fuel, alternatives and known traffic delays

Protect an operational margin beyond the minimum

Legal reserve is a floor. Add a deliberate margin for forecast error, routing changes, departure delay, vectors, holding, a missed approach and a less favorable alternate. Verify that the resulting load remains within weight/balance and takeoff/climb limits. If fuel and payload cannot support the plan, use a fuel stop, reduce payload, delay or choose another route.

Set a diversion decision point: the latest time/fuel/position at which a chosen safe option remains usable with the desired arrival fuel. Evaluate it before reaching the point. A nearby airport with the same convective line is not a robust alternative simply because it meets forecast minima at filing.

Compare actual fuel used/remaining with expected consumption and elapsed time. Cross-check fuel-flow totals with the known starting usable fuel and other indications under the aircraft's procedures. Recompute ETA, alternate fuel and margin when groundspeed, weather or route changes. A growing headwind affects the remaining plan even if the engine consumes the planned gallons per hour.

§91.103: fuel, weather, alternatives and traffic delays · §91.167: weather-considered fuel requirement · ACS I.C.R7/S2: fuel risk and scenario recalculation

An EFC is a planning estimate, not extra fuel

When assigned an unexpected hold or changed expect further clearance (EFC) time, calculate the projected holding burn and the fuel needed for the next safe option. Use the holding consumption appropriate to the actual aircraft and power/altitude; do not substitute the cruise rate automatically. Include onward route, approach/missed exposure and the protected arrival margin. Ask ATC for a workable plan before the fuel decision point passes.

Fictional recalculation: 24 usable gallons remain. Fuel needed from now through a diversion landing is 8 gallons, and the pilot protects another 8 gallons as the study exercise's chosen arrival margin. That leaves 8 gallons available for delay. At a verified study holding rate of 8 gallons/hour, the mathematical ceiling is 60 minutes; a prudent decision trigger must be earlier to allow clearance changes and uncertainty. An EFC 75 minutes away is inconsistent with that plan.

Under AIM 5-5-15, advise minimum fuel when the supply means undue delay cannot be accepted upon reaching the destination. This advisory does not request traffic priority and is not an emergency declaration. If remaining usable fuel requires priority to ensure a safe landing, declare a fuel emergency and report fuel remaining in minutes. Do not wait for the gauge to reach zero or use a vague “getting low” call.

Replanning also follows an equipment failure that removes the destination or alternate approach. A formally filed alternate that can no longer be flown is no longer the same operational option. Choose and coordinate a usable plan while fuel still supports it.

AIM 5-5-15: minimum fuel and emergency priority · AIM 5-3-8: holding/EFC instructions · ACS III.B.R1/R2: unexpected EFC and minimum-fuel/emergency scenarios

Work the legal test and the changed scenario on the ground

For ground preparation, use an instructor-provided destination forecast, arrival time, candidate approach charts/alternate notes, NOTAMs and aircraft equipment description. Explain whether the destination exception applies, then evaluate each candidate at its own ETA with its procedure-specific criteria. Include a GPS/WAAS contingency.

Build the usable-fuel calculation using stated aircraft inputs, then change the winds, hold time or available approach and recalculate the remaining options. State the latest safe decision trigger and the message to ATC. These activities prepare ACS I.B.S4 and I.C.S2. They do not establish flight performance, actual dispatch legality or the skill assessment required on a practical test.

ACS I.B.S4: ground preparation for alternate determination · ACS I.C.S2: ground preparation for fuel-reserve recalculation · §91.169: regulatory test applied to the scenario

FLIGHT SCENARIO

What would change your plan?