How KeepBlueUp works

A written walkthrough of the same material follows, so nothing here is only available as video.

Every constant and relation in these tools is cited to a published source in the code that uses it: the FAA weight-and-balance handbook and the Pilot's Handbook of Aeronautical Knowledge, each aircraft's own handbook (and its type certificate data sheet, where one is cited) for its limits, the NWS pressure-altitude formula, the FAA and AOPA density-altitude rules of thumb and the ICAO standard-atmosphere density ratio for true airspeed, UK CAA Safety Sense SS09 and SS12 for the grass, slope and safety factors, 14 CFR 91.151 and the EASA and UK CAA AMC1 NCO.OP.125(b) for fuel reserves, and FMH-1, WMO No. 306 and ICAO Annex 3 for the METAR code.

The tools line up with the exam standards: the FAA private pilot standard, FAA-S-ACS-6C (in force since 31 May 2024), and the EASA PPL theory syllabus, AMC1 FCL.210; FCL.215. Which items each tool practises is listed on the about page - practising them is all it claims; nothing here is approved by an authority.

1,239 automated tests run on every build, and the important ones are anchored to a published worked example - the POH's own sample loading problem, its short-field takeoff chart cell by cell, and the FAA pressure-altitude conversion table - so the maths is checked against someone else's answer rather than against itself. The full list is in about.

These are the things the tools deliberately do not do. None of them is a bug, and all of them matter more than the features.

Weight & Balance

• Six aircraft profiles. Cessna 172S Skyhawk SP, Cessna 172N Skyhawk (from the 1978 handbook), Cessna 152, Piper PA-28-161 Warrior II, Piper PA-28-181 Archer II/III and Diamond DA 40. Anything else needs its own profile, which does not exist yet. Each profile is one variant of its type, and variants differ - the aircraft page for each one names the serial-number effectivity and the variants it does not cover, and you must check it matches yours.
• Both certificated categories are modelled where the handbook publishes them, with their own weight limits, their own envelope and their own occupancy restrictions. Utility on the 172S requires the rear seat empty and the baggage compartment empty, and the tool enforces that as a failure rather than a note. The Cessna 152 is certificated in the Utility category only, so there is no normal-category envelope to choose.
• Adjustable seats are modelled as the range the handbook publishes, not a single point - the 172S front seats span 34 to 46 inches and the 152's span 33 to 41. The headline centre of gravity is the average-occupant position, and the tool warns separately when running the seats to one end of their travel would change the verdict. The Piper and Diamond handbooks publish no such range, so those profiles use the single published arm, and a non-standard seat position is not modelled for them.
• The prefilled empty weight and empty-weight arm are placeholders, derived from published handbook data. They are not any real aeroplane. Replace both with the values from the current weight-and-balance record of the aircraft you are flying - this is the single most likely way to get an answer that looks right and is not.
• Equipment changes are not tracked. Supplements, supplemental type certificates and equipment-list changes alter the empty weight and arm. They come to the tool only through the numbers you type.
• Longitudinal balance only. There is no lateral (left/right) balance calculation.
• The takeoff-distance figure is a rule of thumb, not chart data. It applies a fixed percentage increase per 1,000 ft of density altitude - 12% for a fixed-pitch propeller like the 172S, 10% for a constant-speed one. Its source gives those rates up to 8,000 ft and steeper ones above; the tool stops at 8,000 ft, because above it these rates under-state the C172S handbook chart, and sends you to the chart instead of extrapolating an optimistic number. It exists to make the cost of density altitude tangible. Plan a short field on the aircraft's own chart.

E6B

• The maths is done in degrees true. METAR and TAF winds are reported in degrees true; ATIS, tower and AWOS winds and runway designators are magnetic. You can enter a magnetic variation and the tool will give you the magnetic heading alongside the true one, and the crosswind card lets you say which reference your wind is in - but it applies the conversion once, so do not pre-convert and then enter the variation as well. Magnetic deviation, the error of your particular compass, is not modelled.
• Density altitude is a standard-atmosphere approximation (the standard temperature at your pressure altitude, plus about 120 ft per degree Celsius of deviation from it). There is no humidity correction, and it is not certified performance data.
• True airspeed applies no compressibility correction. The error is a tenth of a knot at 110 kt and 7,000 ft and under a knot at 180 kt, so it is negligible across light general aviation. Do not trust it above about 180 kt.
• A wind triangle can have no solution. When the crosswind component exceeds true airspeed the course simply cannot be held, and the tool says so rather than printing a heading.
• Fuel and time are arithmetic on the burn rate you enter. There is no climb, cruise and descent profile. The reserve is the chosen rule's minutes at the reserve burn you enter; climb, descent, expected delays and contingency fuel are yours to add.

METAR decoder

• It decodes the observation, not the forecast. Trend and landing-forecast groups (NOSIG, BECMG, TEMPO, PROB) are shown as raw text, clearly separated and labelled as not decoded, because they describe the future and must never overwrite what was observed. Remarks after RMK are shown the same way.
• TAFs are decoded, and kept apart from the observation. A forecast is a prediction for a future period, so it never contributes to the observation's flight-category badge. Each forecast period carries its own category, labelled as a forecast and scoped to its own time window. Paste a block containing both and you get both, decoded separately.
• The flight category is the US VFR / MVFR / IFR / LIFR convention, computed from ceiling and visibility only. It is a colour-coded shorthand, not a substitute for reading the report - and it is withheld rather than guessed when the report does not carry enough to support one.
• Looked-up reports are relayed, and can be stale. The raw text comes from the NWS Aviation Weather Center; the decode is ours and is not official. Neither is a weather briefing under 14 CFR 91.103. Pasting a report you already have always works, including with no connection.

• Take the empty weight and empty-weight arm from the aircraft's own current weight-and-balance record - never from the prefilled defaults.
• Check the limits and the envelope against the POH or AFM for that serial number.
• Use the aircraft's performance charts for anything runway-related.
• Get an official weather briefing.
• Treat a result here as a cross-check that agrees, or as a prompt to find out why it does not.

KeepBlueUp installs to a phone home screen and the calculators keep working with no connection - useful at a field with no signal. Weight and balance, the E6B and decoding a METAR or TAF you paste all work offline. Looking an airport's weather up by its code needs a connection, and so does the table of the wind on each runway under a decode, which fetches that airport's runways.

On iPhone or iPad: in Safari tap ••• then Share (or the Share button, if your tabs are at the top or bottom), choose Add to Home Screen, leave Open as Web App on, and tap Add. If Add to Home Screen is missing, scroll down and add it under Edit Actions. Chrome, Edge and Firefox on iPhone can do the same from their Share menu. On Android or a computer, choose Install from the browser menu.

Opened from Instagram, TikTok or another app? Its built-in browser cannot install anything, and loadouts saved there stay there - open the page in your phone's own browser first.

Offline use is a convenience, not a guarantee: a cached page can be out of date. Reload when you have signal.

No account, no cookies, and the numbers you type never reach our server - a link you share carries them in the link itself, wherever you send it. The detail is in the privacy policy.

A report that a formula, a limit or a decode is wrong is the most valuable message we get, and it goes to the top of the queue. Include the inputs you used.

contact@keepblueup.com