About KeepBlueUp

KeepBlueUp is built by a licensed private pilot who flies general aviation and films it. That is the whole reason it exists: the tools come from the checks that get done in a real preflight. The clips so far are screen recordings of worked examples on this site, not real trips. Videos from real flights may follow, and if they do, they will say so.

It is not a content farm and not a repackaged calculator. Every formula was written from a cited source and tested before it shipped, because getting a weight-and-balance answer subtly wrong is a different class of mistake from getting a currency converter wrong.

Nothing here is a formula someone half-remembered. Every constant and relation is cited in the source, next to the code that uses it, so it can be checked against the original rather than trusted.

Weight and balance

• Method and datum: FAA-H-8083-1B, Aircraft Weight and Balance Handbook, and FAA-H-8083-25C, Pilot's Handbook of Aeronautical Knowledge, chapter 10.
• Limits, station arms, baggage placards, fuel and the centre-of-gravity envelope: each aircraft's own handbook (POH or AFM) and, where one is listed, its type certificate data sheet, named to the revision. The list below is read out of the aircraft data itself, so it cannot fall out of step with it:
  • Cessna 172S Skyhawk SP: Cessna Model 172S POH / Information Manual, Section 2 (Limitations), Jul 8/98; Cessna Model 172S POH, Section 6 (Weight & Balance / Equipment List); FAA-H-8083-1B, Aircraft Weight & Balance Handbook.
  • Cessna 172N Skyhawk: Cessna Pilot’s Operating Handbook, Skyhawk 1978 Model 172N (D1109-1-13, Change 1), Section 2 (Limitations); Cessna 1978 Model 172N POH, Sections 4, 5 and 6; FAA Type Certificate Data Sheet 3A12, Revision 84, 29 July 2015, Model 172N; FAA-H-8083-1B, Aircraft Weight & Balance Handbook.
  • Cessna 152: FAA Type Certificate Data Sheet 3A19, Revision 50, 21 July 2017 (Cessna 150/152), section IX - Model 152; Cessna Model 152 Pilot’s Operating Handbook, 1978 Model 152, Section 6.
  • Piper PA-28-161 Warrior II (2,440 lb): FAA Type Certificate Data Sheet 2A13, Revision 64, 18 September 2023 (Piper PA-28 series), section XVI-B; Piper PA-28-161 Warrior II POH, Report VB-1180, issued 13 August 1982, Section 6.
  • Piper PA-28-181 Archer II / III: FAA Type Certificate Data Sheet 2A13, Revision 64, 18 September 2023 (Piper PA-28 series), sections XV-A and XV-B; Piper PA-28-181 Cherokee Archer II POH, Report VB-790, issued 18 June 1976, Section 6.
  • Diamond DA 40 (standard tank): Diamond DA 40 Airplane Flight Manual, Doc. # 6.01.01-E, Revision 7, 15 July 2006 (values re-checked against Revision 10, 18 September 2023); EASA Type Certificate Data Sheet EASA.IM.A.022, Issue 24, 22 April 2021 (DA 40).

E6B and performance

• Pressure altitude: the US National Weather Service formula - within about 4 ft of the exact ICAO standard-atmosphere relation below 10,000 ft - not the "1 inch equals 1,000 feet" shortcut, so the inches-of-mercury and hectopascal paths give the same answer for the same weather.
• The ISA temperature and its 2 °C per 1,000 ft lapse rate: FAA-H-8083-25C, chapter 11. Density altitude: the 120 ft per °C rule of thumb, from AOPA's density-altitude guide.
• True airspeed: the standard-atmosphere density ratio (ICAO Doc 7488/3, the US Standard Atmosphere 1976), with the compressibility approximation stated in the source and its error measured.
• Takeoff distance versus density altitude: an instructor's published rule of thumb (12% per 1,000 ft for a fixed-pitch propeller, 10% for constant speed; Sparky Imeson, Mountain Flying), cited as such. The tool stops at 8,000 ft density altitude: its source switches to steeper rates there, and above it the rule under-states the C172S handbook chart, so it sends you to the chart instead.
• Grass, soft ground, slope and the 1.33 take-off safety factor: UK CAA Safety Sense SS09, Weight, Balance and Performance (August 2024), pages 13 and 15. The soft-ground floor, the no-credit rule for a downhill take-off and the ground-roll caution come from Safety Sense SS12, Strip Flying (May 2024), page 15. These replace SafetySense 7c, Aeroplane Performance (January 2013), which the CAA lists as superseded; no factor value changed.
• Demonstrated crosswind and the tailwind correction: each type's own handbook - and where a handbook builds wind into its chart instead of printing a percentage, the tool sends you to the chart rather than inventing one.

METAR

• Report format and code groups: FMH-1 (the US Federal Meteorological Handbook No. 1, chapter 12), WMO No. 306 FM 15 METAR and FM 51 TAF, ICAO Annex 3 for the ICAO-only groups and wind shear, the WMO runway-state code tables 0919, 0519, 1079 and 0366, and NWS Instruction 10-813 for the US TAF forms. A group the decoder does not recognise is named on screen, never silently dropped.
• Flight-category thresholds (VFR, MVFR, IFR, LIFR): FAA AIM 7-1-7 and the NWS Aviation Weather Center's flight-category definitions; a ceiling is a broken, overcast or obscured layer, as 14 CFR 1.1 defines it.
• Raw reports: relayed from the NWS Aviation Weather Center (aviationweather.gov), shown unmodified. The plain-English decode is ours, and is not official.

What the checkride and the theory exam ask

Each tool practises items the FAA private pilot standard and the EASA PPL theory syllabus name. Practising is all it claims - nothing here is approved by the FAA, EASA or any other authority. FAA: FAA-S-ACS-6C, Private Pilot for Airplane Category Airman Certification Standards (November 2023), the standard 14 CFR 61.14(b)(3) has incorporated since 31 May 2024, quoted by element code. EASA: AMC1 FCL.210; FCL.215, which gives the subject headings below but no item codes.

• Weight and balance: PA.I.F.S1 “Compute the weight and balance, correct out-of-CG loading errors and determine if the weight and balance remains within limits during all phases of flight.”; PA.I.F.K2e “Loading [e.g., center of gravity (CG)]”; PA.I.F.K2f “Weight and balance”. EASA: 7.1 Mass and balance: aeroplanes or helicopters.
• Density altitude and takeoff distance: PA.I.F.K2a “Atmospheric conditions”; PA.I.F.S2 “Use the appropriate airplane performance charts, tables, and data.”; PA.I.F.R3 “Possible differences between calculated performance and actual performance.”; PA.VI.A.K5d “True airspeed and density altitude”. EASA: 7.2 Performance: aeroplanes.
• Crosswind on the runway: PA.IV.A.R1 “Selection of runway or takeoff path based on aircraft performance and limitations, available distance, and wind.”; PA.IV.A.R2a “Crosswind”; PA.IV.B.K3 “Wind correction techniques on approach and landing.”; PA.IV.B.S8 “Maintain directional control and appropriate crosswind correction throughout the approach and landing.”. EASA: 7.2 Performance: aeroplanes.
• Fuel and reserves: PA.I.D.K3c “Fuel requirements, including reserve”; PA.I.D.R6 “Fuel planning.”; PA.I.D.S4 “Recalculate fuel reserves based on a scenario provided by the evaluator.”; PA.VI.C.S2 “Make a reasonable estimate of heading, groundspeed, arrival time, and fuel required to the “divert to” destination.”. EASA: 7.3 Flight planning and flight monitoring - fuel planning.
• METAR and TAF: PA.I.C.K2a “Airport Observations (METAR and SPECI) and Pilot Observations (PIREP)”; PA.I.C.K2c “Terminal Aerodrome Forecasts (TAF)”; PA.I.C.R1b “Personal weather minimums”; PA.I.C.S3 “Correlate weather information to make a go/no-go decision.”. EASA: 3. Meteorology - Aviation weather messages.

1,239 automated tests run on every build, and the build refuses to publish if a single one fails. They cover the flight maths, the METAR and TAF decoders, number and unit formatting, the forms themselves (a field the tool cannot read must block the verdict), and the colour palette's contrast in both light and dark themes. The number on this page is counted by the build, not typed by hand.

The tests that matter most are the ones anchored to a published worked example, so the maths is checked against someone else's answer rather than against itself:

• the Cessna 172S POH sample loading problem (section 6, figure 6-5), transcribed with the handbook's own moments, weights and verdict;
• the POH short-field takeoff distance chart (figure 5-5) - every one of its 45 cells, which is how we know the rule of thumb never under-states the chart below 8,000 ft density altitude, and refuses to answer above it;
• the FAA pressure-altitude conversion table, cell by cell;
• the UK CAA take-off example in AIC P 173/2024 (390 m on a paved runway becomes 755 m from an uphill grass strip on a warm day), and the 791 m version of the same example in the superseded SafetySense 7c, which starts from 10 °C instead of 15 °C;
• the wind triangle checked against an independent vector solution at every 5 degrees of relative wind, all the way round, at three wind speeds;
• real METARs, including the awkward ones - variable winds, missing visibility, vertical visibility, trend groups that would otherwise overwrite the observation and turn a low-IFR report green.

Found something wrong? That is the most useful email we get. Tell us and include the inputs.

Every change that altered an answer a pilot could have acted on, newest first. Your printed sheet carries the build it came from (top right of the sheet: 25787a2 · 2026-10-12), so it can be checked against this list.

To hear about the next one without checking back, follow the Atom feed of this log in any feed reader.

1. 2026-10-12 · Weight & balance

   Was: Fix my load's "carry less fuel" suggestion counted no start and taxi fuel on the C152, PA-28-181 and DA 40, which have no start and taxi figure built in, so the fuel it said the aeroplane lands with was high by whatever starting, taxiing and taking off burn. A DA 40 on the illustrative airframe (1,620 lb at 94.3 in) with 380 lb in front, 340 lb behind, 20 lb of baggage and full tanks, on a 15 gal trip with a 7.7 gal final reserve, read "Carry 17.5 gal less fuel - lands with exactly your 7.7 gal reserve" - under the reserve once any fuel is burnt before takeoff.

   Now: On those three types no fuel cut is offered: the card says less fuel might fix it, but that with no start and taxi figure built in the tool cannot check what a lighter load lands with. The C172S, C172N and PA-28-161 subtract their handbook's start and taxi figure before the trip and the reserve, and still offer one.

2. 2026-10-12 · E6B

   Was: For a variable wind (VRB) with a gust, the crosswind card's worst-case tailwind used the steady speed: VRB08G14KT on the C172S read "a tailwind of up to 8 kt" and about +40% on the takeoff distance, although the 14 kt gust can be behind you too - past the 10 kt the POH tailwind note covers.

   Now: The worst case is the gust: 14 kt behind, past the POH note, where the card says there is no published correction.

3. 2026-10-12 · Weight & balance

   Was: A load exactly on a limit could fail after switching the entry units to kg and litres, because the switch rounds every field to two decimals: a C172S with its full 53 US gal of usable fuel (200.63 L) read "318.0050331876919 lb exceeds its 318 lb limit", and one loaded to exactly its 2,558 lb maximum ramp weight read "Over maximum ramp weight: 2558 lb exceeds 2558 lb limit". Full PA-28 tanks (48 gal, 181.7 L) and a full C172S baggage area 2 (22.68 kg) did the same.

   Now: Placards, combined limits and the ramp, takeoff and landing limits allow that rounding - 0.02 lb (9 g) per field - so these loads stay within limits after the switch. A real excess still fails.

4. 2026-10-12 · Weight & balance

   Was: In kg and litres, the maximum shown beside a station was rounded to the nearest kilogram, or tenth of a litre, and could read above the placard: C172S baggage area 2 showed "max 23 kg" for 22.68 kg and the DA 40 fuel "max 152.2 L" for 152.17 L, and entering the number shown failed the check.

   Now: A station maximum shown in kg or litres is rounded down, so the number shown can always be entered.

5. 2026-10-12 · Aircraft data

   Was: The Cessna 172S page said its aft CG limit binds before its weight limit - that two adults up front, two in the back and "any baggage at all" run the CG past 47.3 in before the aeroplane is overweight - and that running the front seats full aft moves the CG "about 9 in aft per pound" of front-seat load.

   Now: Rewritten from the profile's own figures, which a test now recomputes: on the illustrative airframe (1,663 lb at 40.0 in), four 170 lb adults and a 20 lb bag reach the 2,550 lb maximum with 32.5 gal on the ramp at a CG of about 45.0 in, 2.3 in inside the aft limit; the same four with 70 lb in baggage area 1 and 50 lb in area 2 are at about 47.4 in, past it with any fuel. Running the front seats full aft moves 340 lb of occupants 9 in, about 1.3 in of CG at 2,300 lb. No limit or figure changed.

6. 2026-10-12 · E6B

   Was: The density-altitude card took any number as an altimeter setting. QNH 1013 typed while the unit still read inHg - at a 5,000 ft field and 30 °C, with the default C172S, the worked example's 960 ft POH ground roll and the 1.33 safety factor - gave a density altitude of -164,079 ft, no takeoff penalty and a 1,277 ft ground roll to plan with; at 29.92 inHg the same field is 8,000 ft density altitude and about 2,503 ft. A wind direction past 360 was read as its remainder: 400 as 040.

   Now: An altimeter setting outside 850-1,100 hPa (25.11-32.48 inHg) is refused with a reason and gives no answer, and hPa digits under inHg say to switch the unit. The crosswind and wind-triangle cards refuse a wind direction outside 0-360.

7. 2026-10-12 · E6B

   Was: With the taxi field left blank, "Least fuel to start with" counted no start, taxi and run-up fuel for the C152, PA-28-181 and DA 40, whose handbooks publish no allowance: a DA 40 flying 85 nm at 98 kt and 8.5 gph under the FAA day rule with 12.0 gal on board showed "0.4 gal more than the minimum", and any taxi burn over 0.4 gal made it a shortfall.

   Now: For those types a blank taxi field is missing, not zero: the card asks for your taxi and run-up fuel before it gives a minimum or a margin. Types whose handbook publishes an allowance still use it.

8. 2026-10-12 · E6B

   Was: At a negative density altitude the true-airspeed card said "+-3 kt over your indicated CAS" (CAS 100 kt at -2,000 ft), although true airspeed there is 3 kt below the CAS.

   Now: It says "3 kt under the CAS you entered", and "+N kt over the CAS you entered" when true airspeed is higher.

9. 2026-10-12 · METAR / TAF

   Was: A runway-state group with a measured friction coefficient from 0.00 to 0.29 - ICAO's "poor" and "medium to poor" bands, the conditions braking codes 91 and 92 name in words - was a plain line in the decode, while codes 91 and 92 went into the "Reported at the runway" warning. Ice with a friction coefficient of 0.25 raised no warning.

   Now: A measured coefficient of 0.29 or less, 0.00 included, goes into that warning too, on the bands of ICAO Doc 9137 Part 2, Table 4-1. The number is still shown as reported, with no braking word added.

10. 2026-10-12 · METAR / TAF

    Was: On the TAF timeline, a change at a part hour (FM120830) was drawn from the start of its hour, so an improvement showed its better category early: a forecast of LIFR until 08:30Z read VFR from 08:00Z. The period list below the timeline gave the right time.

    Now: The hour an FM falls in shows the worse of the two forecasts, and the new one stands alone from the next whole hour - the same rule as during a BECMG change.

11. 2026-10-12 · METAR / TAF

    Was: With a variable wind direction (dddVddd), the wind-on-each-runway table resolved only the mean direction: EGLL 27018G28KT 210V330 showed 0 kt across runway 27R, although at either end of the reported range about 24 kt of the gust is across it.

    Now: Across shows the most crosswind anywhere in the reported range, steady and gust, and a tailwind the range can bring is named. The link that checks the runway in the E6B sends the direction with the most crosswind, and says which.

12. 2026-10-12 · METAR / TAF

    Was: An Australian TAF group PROB30 INTER or PROB40 INTER was headed "PROB30 TEMPO" and explained as temporary fluctuations, on the forecast card and the timeline - although an INTER spell is the shorter one, under 30 minutes (Bureau of Meteorology).

    Now: It is headed as coded, PROB30 INTER, and explained as a probability of intermittent spells under 30 minutes.

13. 2026-10-07 · METAR / TAF

    Was: A runway-state group with braking code 00 - a measured friction coefficient of 0.00, the worst there is - was listed as not decoded; extent code 1 read "10% or less" where the WMO table says "less than 10%"; and a TAF PROB30 was described as "30 to 39 percent", a band no ICAO text gives.

    Now: Code 00 decodes as friction coefficient 0.00, extent 1 as less than 10%, and PROB30 / PROB40 as the probability coded. The decoders' sources were re-checked against FMH-1, WMO-306, ICAO Annex 3 and NWS Instruction 10-813.

14. 2026-10-07 · Aircraft data

    Was: The PA-28-181 page cited a "POH Section 6.2" loading form that is really a retyped training transcription (it says it is not a POH), and its example empty weight (1,541.2 lb at 87.5 in) was one aircraft's own figure from that document, not the handbook's sample.

    Now: Cited to the Archer II POH, Report VB-790, Figure 6-11 (same arms and footnote); the example empty weight is the POH sample loading problem, Figure 6-9: 1,547.0 lb at 86.4 in.

15. 2026-10-07 · Aircraft data

    Was: The PA-28-161 page did not say that a Warrior II with Piper Kit 88050 (the 2,325 lb gross weight modification) is limited to 2,325 lb takeoff and 2,332 lb ramp, so such an aeroplane could be shown within limits up to 2,440 lb.

    Now: The page names the kit and its limits (TCDS 2A13 NOTE 26). Superseded data-sheet revisions are updated (2A13 Rev 64, 3A19 Rev 50; no figure changed) and the FAA handbook link, which had moved, is fixed.

16. 2026-10-07 · Aircraft data

    Was: The Diamond DA 40 page named only the modified main-gear strut (MAEM 40-123/e) as raising the maximum landing mass from 2,407 lb to 2,535 lb, although the tall main-gear strut (OÄM 40-283) does too - an owner with that strut was not told; and it gave the datum in the type certificate's words, not the flight manual's.

    Now: The page names both modifications (EASA TCDS Note 10) and quotes the AFM's datum (Section 2.8). The modelled limits did not change: 2,407 lb landing for the original strut, and a ramp limit equal to the 2,535 lb takeoff mass - stricter than the 2,544 lb ramp mass the AFM allows where a flight is defined to begin at engine start.

17. 2026-10-07 · E6B

    Was: The grass, soft-ground, slope and 1.33 safety factors were cited to UK CAA SafetySense 7c (January 2013), which the CAA now lists as superseded, and the page said there was no published factor past a 2% uphill slope, although the current leaflet gives x1.1 for every 2%.

    Now: Cited to UK CAA Safety Sense SS09 (August 2024) and SS12 Strip Flying (May 2024). No factor value changed; past 2% uphill the tool still gives no number, and now says why.

18. 2026-09-29 · Aircraft data

    Was: On the Diamond DA 40, full usable fuel (40.2 gal = 241.602 lb) was reported as exceeding the fuel station limit, which had been rounded to 241.6 lb.

    Now: The limit is the exact 40.2 gal x 6.01 lb/gal, and a test checks full tanks on every aircraft.

19. 2026-09-29 · Weight & balance

    Was: A number the form could not read - "38,5" on a European keyboard, or text - counted as zero under a green verdict.

    Now: Any unreadable, ambiguous ("1,663") or implausible field blocks the verdict and says which field and why.

20. 2026-09-29 · E6B

    Was: Every pilot was measured against the Cessna 172S demonstrated crosswind (15 kt) and its tailwind note, whatever they flew - 13 kt read as comfortable for a C152, whose figure is 12 kt.

    Now: The aircraft picker sets the demonstrated crosswind, the tailwind correction and the takeoff rule of thumb from that type's own handbook.

21. 2026-09-29 · METAR / TAF

    Was: Groups the decoder did not recognise were dropped without a word, and a mistyped cloud group (BKN0015) could leave a VFR badge. Automated "//////CB" lost the cumulonimbus.

    Now: Unrecognised groups are listed as "Not decoded", an unreadable cloud group makes the category unknown, and CB/TCU are always named. Wind shear and runway state are decoded; the report's age is shown.

22. 2026-09-29 · E6B

    Was: The takeoff estimate assumed a dry, level, paved runway and no safety margin.

    Now: Grass, soft ground, slope and the 1.33 safety factor from UK CAA SafetySense 7c can be applied, and steeper than 2% returns no number.

23. 2026-09-06 · Weight & balance

    Was: Only the normal category was modelled, and adjustable seats sat at one point - a C172S load could read "within limits" and be outside the aft limit with the seats legally full aft.

    Now: Utility category per airframe with its restrictions enforced, and the handbook seat range checked end to end.

24. 2026-09-01 · E6B

    Was: The takeoff rule of thumb used the constant-speed 10%/1,000 ft rate on fixed-pitch aeroplanes and extrapolated past 8,000 ft density altitude - up to 19% short on required runway.

    Now: 12%/1,000 ft for fixed pitch, 10% for constant speed, and no answer above 8,000 ft.

25. 2026-09-01 · Weight & balance

    Was: A load containing an invalid number returned "within limits" with no violations, and ramp weight was checked against the maximum takeoff weight.

    Now: Fails closed on any non-finite input; ramp, takeoff and landing are checked separately, as the POH does.

26. 2026-09-01 · METAR / TAF

    Was: Trend groups (BECMG, TEMPO) were read as the observation - a real low-IFR report could show green VFR - and a pasted METAR plus TAF merged into one decode.

    Now: The trend is kept apart and never feeds the category; each report is decoded on its own.

Said plainly, because it matters more than anything else on this page.

• Not a substitute for the POH or AFM. The handbook for the specific serial number you are flying is the authority. This is a cross-check.
• Not your aircraft. The prefilled empty weight and empty-weight arm are documented placeholders. Take both from the current weight-and-balance record of the aeroplane in front of you, every time.
• Not an electronic flight bag, and not approved or certified by EASA, the FAA or anyone else. There is no approval regime for a general-aviation planning website, and we claim none.
• Not a weather briefing. A decoded METAR is not preflight action under 14 CFR 91.103.
• Not performance chart data. The takeoff-distance figure is a rule of thumb for intuition, not a number to plan a short field on.
• Not an authorisation to fly. You are the pilot in command.

The full list of limits, tool by tool, is on the help page.

Today: it is not. There are no advertisements, no affiliate links, no sponsored placements and no commercial relationship with any retailer, training provider or manufacturer. There is no paid tier and no account.

If that ever changes, the rules are already written down: disclosure right next to any link that could earn us a commission, never any commercial content inside or beside a result, and no money that could change a calculation. See section 12 of the terms and section 12 of the privacy policy.

KeepBlueUp is operated by Gaperi Consult S.R.L., a company registered in Romania with its registered office in Brasov. The full trader-identification details are in section 1 of the terms. Contact: contact@keepblueup.com.