Why mass & balance matters

Every aircraft has a Maximum Take-Off Mass (MTOM) and a Maximum Landing Mass (MLM), plus a Centre of Gravity (CG) envelope that must be respected on both take-off and landing.

Exceed the mass limit, or let the CG fall outside its envelope, and you compromise structural limits, stall speed, controllability and stopping distance.

As Pilot in Command you are legally responsible for confirming the aircraft is loaded within limits before every flight - this is not optional paperwork.

The basic mass equation

Basic Empty Mass (BEM) is the aircraft plus unusable fuel, oil and fixed equipment, taken from the aircraft's weighing schedule.

Add all the 'loaded items' - crew, passengers, baggage, and usable fuel - to BEM to get Take-Off Mass.

Take-Off Mass minus fuel burned in flight gives Landing Mass; always check this against MLM separately, not just MTOM.

Fuel mass conversion: Avgas is approximately 0.72 kg/litre (roughly 2.2 lb/litre) - always confirm the exact figure from the POH/AFM, as it varies slightly by fuel type and temperature.

Working out the Centre of Gravity

Each loaded item has an 'arm' - its distance from the datum (a fixed reference point, often the aircraft nose or firewall).

Moment = Mass x Arm, for every item, including the empty aircraft.

Total Moment / Total Mass = CG position - this must fall inside the forward and aft CG limits published in the POH/AFM loading chart or CG envelope graph.

Many light aircraft use a loading chart or graph rather than raw arithmetic - learn to read both, since exam questions test either method.

Fuel burn during flight

As fuel burns off, mass decreases and CG typically shifts (usually forward, since fuel tanks are often ahead of the CG) - always check the CG position at both take-off AND landing, not just take-off.

Some aircraft have a CG envelope that narrows at lower masses - a loading that's fine at MTOM might be out of limits after burning most of the fuel.

Common mistakes

• Forgetting unusable fuel is already included in BEM - don't add it again.
• Mixing up units - always convert consistently to kg or lb, and litres to mass correctly.
• Checking only the take-off CG and ignoring the landing CG.
• Using the wrong datum or arm sign convention (arms aft of datum are usually positive, forward are negative - check the specific aircraft's convention).
• Rounding too early in multi-step moment calculations, which compounds errors.
• Forgetting baggage compartment limits - many aircraft have a maximum baggage mass separate from the overall mass limit.

Exam technique

Always draw out a simple table: Item | Mass | Arm | Moment, then sum the Mass and Moment columns before dividing.

Double-check your final CG position lands inside the envelope, and always verify both take-off and landing conditions when fuel burn is significant.

Why take-off and landing performance matters

Before every flight you must prove the aircraft can safely get airborne and stop again on the runways you plan to use. This isn't guesswork - it comes straight from the Pilot's Operating Handbook (POH) or Aircraft Flight Manual (AFM) performance graphs and tables, and it's examinable on the CAA Flight Planning paper.

The core factors that change your distances

• Pressure altitude - higher airfields mean thinner air, less lift and less power, so distances grow.
• Temperature - hotter air is less dense, so ISA deviations above standard increase distances significantly (density altitude effect).
• Runway slope - an upslope lengthens take-off roll and shortens landing roll; a downslope does the opposite.
• Wind component - headwind shortens distances, tailwind lengthens them dramatically. As a rule of thumb, only ever apply 50% of a reported headwind and 150% of a reported tailwind for safety margins - many POH tables state this factor directly.
• Runway surface - grass, wet or contaminated surfaces increase both take-off and landing distances; POHs typically add a percentage for grass (often 10-25%) and more for wet grass.
• Aircraft mass - heavier aircraft need more distance to accelerate to unstick speed and more distance to stop.

Key definitions you must know cold

• TODA (Take-Off Distance Available) - the full runway plus any clearway.
• TORA (Take-Off Run Available) - the physical runway length available for the ground roll.
• ASDA (Accelerate-Stop Distance Available) - TORA plus any stopway.
• LDA (Landing Distance Available) - the runway length declared available for landing.
• Take-off distance required - to a screen height of 50 feet, taken straight from the POH graph for the day's conditions.
• Landing distance required - from 50 feet screen height to a full stop, again read from the POH.

Applying safety factors

Regulations require margins beyond the raw POH figures. For public transport-style planning the common factor is landing distance required multiplied by 1.43 (roughly a 43% safety margin) to determine the LDA needed, though for PPL/private ops always check what factor the specific question or POH demands - do not assume one factor fits every scenario.

Common mistakes to avoid

• Forgetting to interpolate correctly between graph lines for temperature, altitude and mass - always read graphs methodically, one variable at a time, following the reference lines exactly as printed.
• Applying the wrong wind correction (mixing up the 50/150 rule).
• Ignoring density altitude on hot, high airfields - a classic trap in exam questions.
• Confusing TODA, TORA and ASDA when checking a runway is suitable.
• Forgetting that wet or grass surfaces need factoring even when the raw calculation shows enough runway.

Exam technique

Always work through POH graphs step by step exactly as the manufacturer intends, note the pressure altitude and OAT (or ISA deviation) first, then mass, then wind and surface corrections last.

Cruise performance and range

Cruise performance links power, speed, fuel flow and altitude. For PPL flight planning you need to pull numbers from the POH/AFM performance tables or graphs and apply them correctly, not just look them up blindly.

Power settings and speed

• Cruise power is usually quoted as a percentage of maximum continuous power (eg 55%, 65%, 75%).
• Higher power gives higher True Airspeed (TAS) but burns more fuel per hour, so range and endurance both fall.
• 75% power is a common training cruise setting - a reasonable balance of speed and economy.
• POH tables give TAS and fuel flow for combinations of power setting, altitude and outside air temperature (OAT); always cross-check the OAT column, since a non-standard temperature changes the figures.

Altitude effects

• As altitude increases, air density falls, so for a fixed power setting TAS tends to rise (less parasite drag) while fuel flow for that % power stays roughly similar - meaning specific range (nautical miles per gallon/litre) often improves with altitude, up to the aircraft's normal operating ceiling.
• Higher altitude cruise can also mean better tailwind components - always check forecast winds at different flight levels when planning.
• Best range is normally achieved at a specific speed close to the aircraft's best lift/drag speed; flying faster or slower than this burns more fuel for the same distance.

Range and endurance

• Range = the distance you can fly on the fuel available; endurance = the time you can stay airborne.
• Maximum range power settings are lower than maximum speed settings - if range matters more than time, throttle back.
• Maximum endurance uses the lowest fuel flow setting, normally slower than best range speed.
• Always plan fuel using actual POH fuel flow figures, not rounded 'rule of thumb' numbers, and always include CAA-mandated reserves (typically final reserve fuel is planned separately from trip, taxi, contingency and alternate fuel in the flight plan).
• Wind has a major effect on range over the ground - a headwind reduces groundspeed and effective range, a tailwind extends it, even though TAS and fuel flow are unchanged.

Common mistakes

• Using TAS figures from the wrong power/altitude/temperature row in the table.
• Forgetting that fuel flow (and therefore range) changes with power setting, not just with altitude.
• Ignoring wind component when converting TAS-based range into a still-air distance versus actual ground distance achievable.
• Confusing best range speed with best endurance speed - they are different numbers with different purposes.
• Not applying reserves on top of trip fuel when calculating how far the aircraft can safely go.

Why fuel planning matters

Running short of fuel is one of the most preventable causes of accidents in light aviation. UK CAA rules (via EASA-derived Air Ops / SERA-based practice for non-commercial flights) require every flight to carry enough fuel to complete the planned flight safely AND cover the unexpected - diversions, headwinds stronger than forecast, holding, or a go-around.

The standard fuel elements

A proper fuel plan is built from several named elements, each with its own purpose:

• Taxi fuel - covers start, taxi and run-up before departure; usually a fixed allowance from the POH/checklist.
• Trip fuel - the fuel burned from take-off to landing at the planned destination, based on cruise burn rate and time.
• Contingency fuel - normally 5 percent of trip fuel (or a minimum of 5 minutes at holding speed), to cover deviations from the planned burn or route.
• Alternate fuel - fuel needed to fly from the destination to a suitable alternate aerodrome, if one is required.
• Final reserve fuel - the untouchable safety margin. For VFR flights this is fuel to fly for 30 minutes at holding speed (45 minutes for night VFR). This must NEVER be planned to be used in normal operations.
• Additional/extra fuel - any further fuel the pilot judges prudent, e.g. known weather risk or busy airspace delays.

The golden rule

Final reserve fuel is a reserve, not a target. If you land with only final reserve remaining, that is the absolute minimum acceptable - not something to plan towards. Good planning leaves a genuine buffer above this.

When is an alternate required?

An alternate is required unless the forecast weather at the destination, for a reasonable margin either side of the ETA, clearly shows the aerodrome will be usable (ceiling and visibility comfortably above landing minima) and there is no other reason (e.g. single runway, NOTAM) making a diversion likely.

Common exam traps

• Forgetting that contingency fuel is a PERCENTAGE of trip fuel, not a flat number.
• Mixing up VFR day (30 min) and VFR night (45 min) final reserve figures.
• Treating final reserve as fuel you are allowed to plan into your trip - you are not.
• Forgetting taxi fuel when working backwards from full tanks to work out endurance.
• Not converting between litres, US gallons and kg correctly - always check units before calculating mass and balance.

Practical approach

Always calculate: Taxi + Trip + Contingency + Alternate (if required) + Final Reserve = Minimum fuel required. Compare this to usable fuel on board, not total tank capacity, since some fuel is always unusable.

What NOTAMs actually are

A NOTAM (Notice to Airmen) is a timely warning of changes to aeronautical facilities, services, procedures or hazards that you need to know about before you fly.

They cover things a chart can't show quickly enough - a closed runway, unlit crane, parachute drop, danger area activation, GPS jamming trial, or unserviceable navaid.

NOTAMs are temporary by nature. If something becomes permanent it eventually gets folded into the AIP instead.

Structure and Q-codes

Each NOTAM has a series of numbered items (A to X) covering location, validity period, and the affected area, but the two items examiners love are B and C.

Item B is the start date/time and Item C is the end date/time, both given in UTC using an 8-figure format (year-month-day-hour-minute).

The Q-line uses a Q-code starting QXXXX which tells you the subject and status at a glance once you know the pattern, though in the exam you are not expected to decode obscure codes from memory - focus on reading B, C and the plain-language text.

NOTAMs are graded by scope - some are aerodrome-specific, some are en-route/national, and some (like a temporary danger area) matter hugely to VFR planning.

Where to get them

In the UK, NOTAMs and the AIP are published through the NATS AIS website (some material behind free registration).

Before any flight you should check NOTAMs for your departure, destination, alternate(s) and the route you intend to fly - not just the departure airfield.

A PPL candidate is expected to know that self-briefing is the pilot's responsibility - there is no automatic delivery of NOTAMs to you, you must actively pull them.

The AIP (Aeronautical Information Publication)

The AIP is the master reference for a state's aviation system: GEN (general/legal), ENR (en-route - airspace, danger areas, ATS routes) and AD (aerodrome data - each airfield's own entry with frequencies, runway data, circuit height, hours).

AIP Supplements cover longer-duration temporary changes (weeks/months) that are too substantial for a routine NOTAM but not yet permanent - a classic exam trap is picking 'NOTAM' when the scenario describes something lasting several months, which should be a Supplement.

AIC (Aeronautical Information Circular) carries administrative or explanatory info that isn't safety-critical enough for a NOTAM - things like a new rule explanation or an event notice.

Common exam traps

• Confusing NOTAM (short-term, urgent) with AIP Supplement (longer planned change) with AIC (background information, not operational).
• Forgetting NOTAM times are always UTC/Zulu, never local.
• Assuming a permanent change stays as a NOTAM forever - it should migrate into the AIP at the next amendment.
• Not checking NOTAMs for the alternate and the route, only the destination.
• Treating a PIB (Pre-flight Information Bulletin) as optional - it is the standard document a pilot self-briefs from and should be retained as part of flight planning records.

Why weight matters

Every aircraft has a Maximum Take-Off Weight (MTOW) set by the manufacturer and stated in the POH/Flight Manual. Going over this limit is illegal and dangerous - it degrades climb performance, increases stall speed, extends take-off and landing distances, and can overstress the structure.

Before every flight you must complete a mass and balance (weight and balance) calculation: basic empty weight + crew + passengers + baggage + fuel = total weight, checked against MTOW, and the centre of gravity (CG) checked against the forward and aft limits on the loading chart or envelope. An aircraft can be under MTOW but still unsafe if the CG is out of limits - too far forward makes it nose-heavy and hard to flare, too far aft makes it unstable and can lead to an unrecoverable stall/spin.

Density altitude

Aircraft performance depends on air density, not just height above sea level. Density altitude is pressure altitude corrected for temperature deviation from the International Standard Atmosphere (ISA), which assumes 15C at sea level and a lapse rate of 1.98C (round to 2C) per 1,000 ft.

• High density altitude (hot, high airfields, low pressure) means thin air.
• Thin air means less lift, less propeller/engine efficiency, and longer take-off runs.
• Rule of thumb: for every 1,000 ft of density altitude increase, take-off distance can increase by roughly 10 percent or more (always check the actual POH graphs/tables - never estimate on the day).
• High density altitude also raises true airspeed for a given indicated airspeed, and reduces climb rate.

Pressure altitude is found by setting 1013 hPa (1013.25 mb / QNE) on the altimeter subscale and reading the height shown.

Safety factors

Performance figures in the POH are usually based on a new aircraft, a skilled test pilot, and ideal conditions - a paved, dry, level runway with no wind. Real-world flying never matches this exactly, so safety factors are applied:

• A common guideline is to add 1.33 (33 percent) as a safety factor to POH take-off and landing distances for training/touring flights, though the exact factor depends on the operator, aircraft, and any applicable regulation - always check what your specific exam question or POH specifies.
• Additional distance must be added for a grass, wet, or contaminated runway, a runway slope, or a tailwind component.
• A tailwind has a much bigger effect on take-off/landing distance than an equivalent headwind reduces it - so tailwind corrections are usually a steeper multiplier in POH graphs.

Common mistakes

• Forgetting that MTOW checks and CG checks are two separate requirements - both must pass.
• Confusing pressure altitude with density altitude - density altitude also needs the temperature correction.
• Reading POH performance graphs without applying the safety factor, or applying it to the wrong figure (distance, not speed).
• Ignoring that fuel burn changes weight and CG throughout the flight, especially on longer trips.
• Using true airspeed instead of density-altitude-adjusted figures when working out actual ground performance.