What assumptions make an educational flight calculation reproducible?

What a reproducible record contains

Every Crabwise result comes from a short chain of formulas, and the step-by-step view shows each formula with the values substituted. A result someone else can check needs that chain plus the meaning of every input: the unit, the north reference for angles, whether an altimeter setting was entered in inHg or hPa, which fuel density was assumed, and whether a speed was indicated or calibrated.

The app also lets you choose values that are assumptions by design, such as the reserve minutes on the fuel screen or the planning density on the unit screen. Write them down next to the answer, because the same number with a different assumption is a different calculation.

Worked example

The independent scale check is 24 × 5 = 120 NM per hour. It establishes arithmetic consistency for the supplied distance and time, not measurement accuracy.

Arithmetic ground-speed check (kt)

120

Build the record

1. Name the screen and mode, for example the altitude screen's density-altitude calculation.
2. List each input with its unit and source, and mark which are observations and which are assumptions.
3. Copy the intermediate steps that matter, not just the last line.
4. Repeat one step by hand as an arithmetic check.
5. Keep failed or unavailable results in the record instead of replacing them with zero.

A density-altitude record

Inputs: field elevation 2000 ft, altimeter 30.12 inHg, OAT 25°C. Pressure altitude is 2000 + (29.92 − 30.12) × 1000 = 1800 ft. The ISA temperature at that level is 15 − 1.98 × 1.8 = 11.436°C, so the deviation is 13.564°C. The pressure ratio is about 0.936643, the temperature ratio about 1.034704 and the density ratio about 0.905228, giving a density altitude of about 3363.197435 ft.

Pressure altitude (ft)

1800

ISA deviation (°C)

13.564

Density ratio σ

0.905228

Density altitude (ft)

3363.197435

A hand check of the first step, −0.2 × 1000 = −200 ft, confirms the subtraction but not the observations.

Common mistakes

• Saving only the final density altitude without the setting or temperature that produced it.
• Leaving out that the setting was typed in hPa and converted to inHg by the app.
• Recording a rounded intermediate value and then using it as the input for a later calculation.

What a log proves

A complete record shows that the arithmetic is consistent with its inputs. It does not show that the observations were correct or that a flight decision follows from them. The FAA navigation chapter and the NIST conversion table below are the references for the formulas and unit definitions used.

Primary sources and related work

• FAA Pilot’s Handbook: navigation and basic flight calculations
• NIST SI conversion factors