QF32 Book – Glossary (not in the QF32 book)

A glossary is not included in the QF32 book because it would take up valuable space at the expense of a more complete QF32 story.  Please contact us if you would like any definitions included in this list.

Glossary by Sections:

Glossary by (key) Alphabetical Listings

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General

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Alpha Also called Angle of Attack (AOA) or Incidence. The angle between the wing chord line and the Free Stream
Angle of Attack (AOA) The local angle between the incident airflow and the chord (or suitable reference) of the wing.
Aspect Ratio (AR) The ratio of the wingspan (b) to the chord (c). Calculated as: b2/wing area.
Auxiliary Power Unit (APU) The A380’s APU is a gas turbine engine located in the rear cone of the aft fuselage. The A380’s APU provides:

  • bleed air to power pressurisation, air conditioning, engine starting services
  • electrical power (3 phase, 115 volts AC at 400 Hz) as a backup power supply for the aircraft’s electrical systems. Each of the two generators can technically provide 120 KVA at sea level, reducing to just 40 kVA at 43,000 feet. Practically, the lower power capability at height is insufficient, so the Operations Manual prohibits the use of the APU in flight above 22,500 feet.

Interestingly:

  • the A380’s APU is almost identical to the Boeing 747’s APU. Both use “PW98x” series APUs, provided by P&W Canada.
  • The APU burns 580 kg of fuel per hour (12 litres per minute).
Induced Drag Varies as a function of 1/AR
By-Pass Ratio The ratio of the air that passes through the fan exhaust (ie not through the engine core) to the air that passes through the engine core. Changes with engine rpm, aircraft speed and altitude.
Bleed Air Air vented from the engine compressor. Generally referred to as LP, IP or HP Bleed (depending if the air is vented from the Low, Intermediate or High Pressure Compressor respectively)
Buffet Margin  The amount of “g” which can be applied before the onset of buffet
CFD Computational Fluid Dynamics.  A computer method to analyze and solve problems that involve fluid (and gas) flows.
Compressibility Aerodynamic effects associated with high-speed flight (> M0.5) due to changes in air pressure and density, that cause the CAS to over read. EAS is used instead of CAS when correction for compressibility is required.
Controlled Flight into Terrain (CFIT) A category of incident where an aircraft is unintentionally but steadily flown into the ground, water or an obstacle.
Dihedral The angle between the lateral axis of an airplane and a line that passes through the center of each wing.
Drag For a moving wing, the component of the resulting force parallel to the wings chord line.
EASA European Aviation Safety Agency. Regulates civil aviation safety for EU member states. Has taken over functions of the Joint Aviation Authorities (JAA)).
FAA Federal Aviation Administration. Regulates civil aviation in the USA. Issues Federal Aviation Regulations (FAR).
Finesse The maximum L/D or “glide” ratio. Also called Slenderness.
Geometrically Limited An aircraft is geometrically limited if, during the ground roll during takeoff, the tail-ground clearance prevents the aircraft from being rotated to the final rotate attitude. All airbus aircraft (except the A318) are geometrically limited) See also VMU.
Fly By Wire (FBW) A system where physical links (cables, rods and cranks) are replaced by electrical signals.  For example, the Airbus A320, A330, A340, A350 and A380 aircraft all have FBW flight controls.  The pilot is one of the many inputs to the aircraft’s many Flight Control Computer (FCCs).  The FCCs process all the inputs, then use kinematic programs to command one or many flight control surfaces to achieve the required result.  Fly by wire aircraft are simpler to design, manufacture, lighter, less costly to built and maintain, and safer than the non-FBW alternatives.  (See big jets book for more information).
Free Stream Air flow uninfluenced by a nearby aircraft.
Induced Drag (Di) Drag resulting from the generation of lift. Also the driving force that creates the horseshoe (leading edge and wingtip) vortex. Induced drag is independent of Mach effects. (CDi Fn C2L/AR)
ISA International Standard Atmosphere:

  • Sea Level: 15 deg C, 1013.25 hPaICAO Lapse Rate = 1.98 deg/1000’ (6.5 °C/km)
  • Dry Adiabatic Lapse Rate = 9.8ºC/km
  • Wet Adiabatic Lapse Rate varies with humidity from about 3.9ºC/1km (26ºC) to about 7.2ºC/1km (-10ºC)
  • Tropopause: 11km, -56.5°C, 226.32 hPa, 0 lapse rate
Kinematics The mechanical study of motion of objects without consideration to the cause of the motion (relevant to Fly By Wire systems)
Laminar The laminar boundary layer is thin, having a low skin speed, lower steady (laminated) accelerated flow and low skin friction. Conversely, a turbulent boundary layer is thicker, has a higher skin speed, greater accelerated flow and more (about three times) skin friction. Turbulent boundary layers remain attached longer in the presence of adverse pressure gradients (ie trailing edge).
Lift The component of the force of a wing normal to the wings chord line. Normally, lift approximates weight. Lift = Cl ½ρV2S
N1,N2,N3 Rotational speed (in % of maximum) of the low, intermediate and high-speed rotors as fitted.
Shock  A thin (few millimeter) discontinuity where a decelerating supersonic flow experiences an increase in pressure, density and temperature. A “normal shock” is perpendicular to the flow. A shock “wave” radiates from the shock with energy that is proportional to the change in Mach across the shock. Wave drag is minimized when the supersonic flow is slowed close to M1 prior to the shock.
Surge Aerodynamic instability in a compressor, normally preceded by a compressor stall, that normally results in reversed airflow in the compressor. May be induced by a high pressure disturbance downstream and/or a compressor failure.
Stall Compressor Stall: In a compressor, the stall of a stage or sector of blades (rotating stall) that results in reduced compressor performance, and may induce a Surge.Wing Stall: A wing is stalled when the angle of attack is greater than the stalling angle. The stall point is the angle at which the coefficient of lift (Cl) reduces as the angle of attack is increased.Aircraft Stall: An aircraft is stall is characterized by some of the following:

  • Buffeting
  • Lack of pitch authority
  • Lack of roll control
  • Inability to arrest descent rate
Wake Turbulence The air disturbance (caused by the pair of horseshoe leg counter-rotating vortices) trailing from a wing that is generating lift.
Wave Drag Drag associated with shock waves and the increased (shock induced) profile drag (disturbed and thickened boundary layer).

Air Traffic Control

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MAYDAY Aircraft & occupants treatened by grave & imminent danger, and/or “I require immediate assistance”
PAN After extensive research over considerable time, I have been unable to find a reliable etymological derivation for this phrase.  The closest I can find is that that ‘PAN’ is derived from the French word  ‘Panne’ which translates as breakdown.Whatever the derivation, Australian authorities describe the phrase “PAN PAN” as an urgent message concerning the safety of the aircraft, vehicle or person “but I do not require immediate assistance”

Computers, Flight Instruments and Avionics

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ADIRS Air Data and Inertial Reference SystemReceives inputs from pitot static, angle of attack and other sensors with internal (inertial and GPS) systems. All sources are weighted for “figure of merit” accuracy to identify the most accurate source. Outputs the most accurate aircraft position, velocity and acceleration to avionic systems.
ADIRU Air Data and Inertial Reference Unit. A computer (normally one of three) that:Accepts inputs from:

  • Air Data references (aircraft probes and sensors)
  • GPS
  • Inertial Reference Unit (with Fibre Optic Gyros)
  • Conducts validity & reliability checks

Outputs to:

  • GP/IRS: attitude, position, speeds
  • Air Data: Pressures, air speed, alt, v/s, Mach, AOA, Temp
ECAM Electronic Centralised Aircraft Monitoring.Provided by the:

  • 2 Flight Warning Systems (comprising many Flight Warning Computers)

Provides:

  • Interactive and dynamic checklists (normal, abnormal and emergency)
  • Procedures
  • Limitations information
  • Status information
  • Altitude Alerts
  • Automated Call Outs

Displayed on:

  • Engine Warning Display
  • System Display (SD)
  • Pilot Flying Display (PFD)
IRU Inertial Reference Unit. Calculates accelerations, velocities and positions for use by navigation systems, flight instruments, radar (for zero elevation) and other systems.All IRUs rely on accurate accelerometers (for linear acceleration) and gyroscopes (for angular velocities). However IRUs can be segmented by their method to derive gyroscopic information:

  • Mechanical gyroscope (Old, least accurate, highest complexity)
  • Ring Laser Gyroscope
  • Fibre Optic Gyroscope (lowest complexity)

The newer solid state Ring Laser and Fibre Optic Gyroscopes detect interference patterns that result from two beams (from the same laser source) combining after travelling in opposite directions around a given path. The interference pattern from three gyroscopes in three axes are used to derive an accurate 3D angular velocity

Crew

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Cabin Service Manager (CSM) The cabin crew member responsible for management of the cabin crew and passengers. The CSM is the most senior person in the aircraft after the pilots.
Captain (Capt) A pilot who is qualified to command the aircraft. The captain of a commercial aircraft will have many aviation licences, aircraft endorsements and approved by the airline company to operate on airline services. There may be many captains in one crew. The captain occupies the left seat in commercial fixed wing aircraft. See also: Pilot-In-Command
First Officer (FO) The Co-Pilot, second-in-command. The FO occupies the right seat in commercial fixed wing aircraft.
Minimum Crew The minimum crew for an A380 is 2 Pilots (pilot and co-pilot)
Pilot-In-Command (PIC) The designated person aboard the aircraft who is responsible under the regulations for the safety of all persons during flight. The PIC has final authority as to the disposition of the aircraft and for discipline for all persons on board. When many Captains are on board, one will be designated the pilot in command. (Australian Civil Aviation Regulation 224). There is no Civil Aviation Regulation that relieves the PIC of his responsibilities.
Second Officer (SO) A pilot carried to augment the crew
Michael von Reth The most professional non pilot crew member I have ever had the pleasure and privilege to work with. Click Here for more information

Fuel

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Flashpoint Temperature (FP) The temperature at which a substance produces vapour rich enough to ignite (in the presence of an ignition source) (Gasoline: -43 deg Celsius. Jet Fuel: 38 to 66 deg Celsius)
Auto Ignition Temperature The temperature at which spontaneous ignition occurs in an ISA atmosphere without an external source of ignition (i.e. flame/spark) (Gasoline: 246 deg Celsius. Jet Fuel: 210 to 245 deg Celsius)

Speeds

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CAS Calibrated Airspeed. Calculated as the Indicated Air Speed (IAS) corrected for position and instrument errors.Old analogue air speed indicators present IAS. Newer ASIs display CAS if:

  • The airspeed value is output from an Air Data Computer (that corrects for position and configuration errors)
  • The ASI is presented on a display that has (by definition) no instrument or parallax errors.
EAS Equivalent Airspeed (EAS) is airspeed that would be displayed on an airspeed indicator that exhibited no errors. Aerodynamicists use EAS when comparing performance, such as Stalling and Gust Values.At sea level (ISA atmosphere): EAS = CAS = TASAt any altitude: EAS = CAS corrected for compressibility error. And TAS = EAS corrected for density.This density increase (compressibility error) increases with TAS squared. This means that the CAS over indicates as airspeed increases.The relationship between EAS and CAS is shown in graph of stall speed (CAS) versus altitude. For a constant EAS stall speed, the compressibility error increases the CAS (due to decreasing temperature and speed of sound) as altitude increases.Having trouble understanding compressibility? Imaging your hand extended outside a jet’s window. At low speeds, you hand feels the stagnation pressure, which is a measure of IAS and CAS. As the speed passes M0.5, the stagnated air starts to compress and become denser, thereby further increasing the stagnation pressure.
F Airbus: Min flap retraction speed during T/O or Go Around
IAS Indicated Airspeed. The speed indicated on the (legacy) airspeed indicator. The total error includes position (pitot static tube location) and instrument errors. The pilot may further induce a parallax error when reading this instrument from an angle.
LRC Long Range Cruise Speed. The speed to maximise the Specific Range to Groundspeed ratio, provides a significant speed increase for 99% of the Max SR
Green Dot Airbus: Dynamically calculated speed that approximates the Best Lift/Drag ratio, and thus the best Climb and Drift Down Performance and approximates the min fuel consumption (
Mach Number The ratio of TAS to the LOCAL speed of sound:Speed of Sound (kts) = 644* √(1+(Temp (°C))/273.15) or more simply,Speed of Sound (kts) = 39 √ (273 + SAT)°C
MDD Drag Divergence Mach number . The speed at which drag increases due to Wave Drag
RN RN = speed x chord x density / viscosityReynolds Number is the scale factor measuring a surface’s influence on a flow. Boundary layers change from laminar to turbulent at a particular RN, so wind tunnels and scale models must have matching RNs to ensure the model’s performance matches the final product. Old naval movies often provide a good examples of miss-matched RNs.
S Airbus only: Minimum speed to retract slats on takeoff
TAS True Airspeed. Calculated as the EAS corrected for density.

  • TAS = EAS in the ISA atmosphere
  • At 40,000’ TAS is approximately equal to twice the EAS.
V1 Decision speed in the event of an engine failure on takeoff at which the aircraft may successfully continue to takeoff or stop. V1 must be greater than VMCG (see Tarpini)
V2 Takeoff Safety Speed. The lowest speed satisfying margins above VMCA and VS/VS1G, and that provides the required climb gradients after takeoff following an engine failure.V2 is always greater than VMCA, ensuring that the aircraft is always controllable. But is usually less than the speed to achieve the highest climb gradient after liftoff. With all engines operating, the climb out at V2+10 provides a higher climb gradient than at V2.It is important for the pilot to understand this relationship. This is the reason that during takeoff, if the airspeed has settled slightly above V2 (engine out) or V2+10 (all engine), that the attitude should be maintained to hold this higher speed and ROC.
Vapp Target speed at 50’ on landing
VC Design cruise speed. One of the speeds used to define the aircraft strength. May be constrained by other speeds such as VDF.
VDF/MDF Maximum demonstrated flight diving speed. The maximum speed demonstrated during certification. A safety margin is required between VC/MC and VDF/MDF. So to permit a cruise at M0.85, the 747, A350 and A380 all required certification with very high VDF/MDFs.
VLOF V Liftoff. The speed at which the aircraft becomes airborne.The aircraft is termed “Geometrically Limited” if the final rotate attitude is greater than the attitude at which the tail strikes the runway.A Geometrically Limited aircraft requires a higher VR, VLOF and thus V2 than a shorter (non geometrically limited) version of the same aircraft.
VLS Airbus: Lowest Selectable Speed.  Minimum operating speed for the autopilot and auto-trim.Dynamically calculated speed (based upon weight, operating engines and configuration) provides a margin against the stall.

  • A380: Minimum value of VMCL2 if two engines inoperative.
VMCA Minimum control speed (a critical engine failed) in the air in a TAKEOFF configuration at which the aircraft can maintain a heading with the rated takeoff thrust, takeoff configuration, gear up and five degrees of bank into the failed engine.Certification requirements only allow for only one engine failure during the takeoff, so VMCA3 will be published for 4 engine aircraft, and VMCA1 for 2 engine aircraft.
VMCL Minimum Control Speed in the air in the APPROACH or LANDING configuration enables (at least): Straight and Level flight then a rolling turn through 20 degrees away from the inoperative engine within 5 seconds.VMCL (all engine) and VMCL-1 (one engine inoperative) will always be publishedVMCL-2 will be published for 4 engine aircraft.
VMCG During a max thrust takeoff , the minimum speed on the ground, at which with the critical engine failed, it is possible to maintain control of the aeroplane with rudder only and remain within 30’ of runway centreline).
VMO/MMO Maximum operating speed/mach number that may not be deliberately exceeded, and is sufficiently below VD/MD, to make it highly improbable that VD/MD will be inadvertently exceeded in operations.
VR Rotation speed. During takeoff, the speed at which the aircraft is rotated for takeoff. The selected VR ensures:

  • in case of an engine failure, V2 is reached at 35’
  • the aircraft lifts off at a speed greater than VMU.
Vs VSTALL or Stall Speed. The speed at which the aircraft exhibits qualities equated to the stall.Some operating speeds were expressed as functions of VS. For example, Vs influences the minimum takeoff (1.2VS) and approach (1.3Vs) speeds, and thus takeoff and landing performance. With this in mind, there was a clear incentive for the manufacturer to obtain the slowest Vs possible. The problem is that when test pilots flew aircraft to determine this speed (with personal pride in obtaining the lowest speed), their “careful” maneuvers resulted in the load factor being less than 1g at the time of the stall.To correct for this anomaly, the certifying authorities required a new stall speed (called Vs1g), calculated at 1g. All aircraft certified after this change publish only the VS1G speeds (not Vs). Older aircraft certified before this change continue to refer to VS.Since Vs1g is always > Vs, takeoff and landing performance would be reduced for newer aircraft using VS1G with the original takeoff and approach minimum speed margins (1.2 and 1.3). To alleviate this problem, certifying authorities defined a VS/VS1G ratio of 0.94 that could be used to factor the speed margins accordingly.Thus when using VS1G, the minimum:

  • takeoff speed is 1.13 VS1G (1.2 x 0.94)
  • approach speed is 1.23 VS1G (1.3 x 0.94)

Practically, all aircraft certified since the mid 1990s use VS1G (ie B747-400 and newer and all Airbus A320, derivatives and newer). Older aircraft continue to use VS (747-100,200,300)
VSR VS1G Stall Speed with a load factor of 1. The speed at which the aircraft exhibits qualities that equate to the stall. VSR (JAR) VS1G (FAR)
VTARGET Airbus:  The target airspeed speed displayed on the air speed tape.  During approach, is equal to the approach speed (Vapp), corrected for wind gusts
VMU Minimum Unstick Speed. The lowest speed at which the aircraft can safely lift off the ground. For Geometrically Limited aircraft, this speed is obtained with the tail of the aircraft touching the runway. By deduction, it is impossible to lift off below VMU.
VLOFHeight Screen Height Heights used in defining takeoff and landing performance.

  • 35’ above the runway for takeoff
  • 50’ above the runway for landing

Heights

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Geometric Altitude  An altitude obtained from a calculation combining:

  • GPS Corrected Altitude
  • Position,
  • GPS ALT Figure Of Merit
Geoid Height The difference between the Earth Geoid (that is MSL +/- 3m) and the WGS84 ellipsoid (GPS floor)

Powerplant

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Under-boost Under-boosting is the condition of an engine having too little compression forces applying on the compression stroke to balance-dampen the forces of the reciprocating metal. Under-boosting any engine is bad.  Engine life will be reduced.  The potential for mechanical failure is increased.   Under-boosting is particularly bad for radial engines, where the master web (that supports all but one of the big end bearings – is also rotating!General handling rules for radial engines require at least 1″ (inch of mercury) of manifold air pressure (absolute) per hundred RPM.

Click here for more information.

Stability

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Longitudinal Control The ability to pitch the aircraft about the lateral axis.  On QF32, the longitudinal axis flight controls all operated normally, however the trapped fuel in the Trimmable Horizontal Stabiliser (THS) caused the aircraft centre of gravity (CG) to be well aft of the normal position.The excess aft position of the CG caused the aircraft to be less longitudinally stable, which would be a factor affecting the flare and landing. (See QF32 page 260.)
Neutral Point The CG position at which the Stick Fixed Static Stability is zero
Stability Positive static stability is the initial tendency for an object (that is in a steady state), that when it is disturbed, will tend to return its previously undisturbed state.
Static Margin The distance of the CG forward of the Neutral Point, measured in a percentage of the wing chord.
Static Stability The tendency for an aircraft disturbed from a steady pitch and attitude to return to that steady pitch and attitude. Static Stability may be further classified as Static Longitudinal, Lateral and Directional Stability.
Stick Fixed Static Stability Static Stability in the configuration where the control surfaces remaining fixed (in their initial trimmed position) throughout the manoeuvre.
Stick Free Static Stability Static Stability in the configuration where the control surfaces are permitted to move throughout the manoeuvre. Indeed, it is the amount of stick force and movement that is measured when determining this stability.
Lateral Control The ability to roll the aircraft about the longitudinal axis. On QF32, the loss of 65% of the ailerons and 50% of the spoilers affected the roll authority. This loss was exacerbated by the three fuel imbalances (from at least ten fuel leaks and failed transfer systems), a holed (venting) wing, uplifting ailerons and spoilers, and severe damage to the wing’s boundary layer (see graph at QF32 after page 278).
Stick A generic term for the pilot’s interfaces to control roll, pitch and attitude. Includes the rudder pedals and either the SideStick in Airbus aircraft or the control yoke in Boeing aircraft.
Relaxed Static Stability The condition with the center of lift forward of the center of gravity instead of aft of it, the airplane would be statically unstable. No matter, though.With artificial stability, the airplane could be more responsive – as much as two and one-half times as dynamic as the F-4C Phantom.  Relaxed static stability allowed the airplane to achieve an initial pitch rate of 5 g’s per second with “deadbeat” damping-no overshoot. Maneuvers could be instantaneously initiated and precisely controlled – a very important factor)

Structures

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Load Factor Ratio of the aerodynamic force (normal to longitudinal axis) to the mass of the aircraft.
Limit Load The maximum loads to be expected in normal operation and without the structure suffering permanently deformation. (Also called “Proof Strength”)The structure may remain deformed if loaded above the Limit Load.
Factor of Safety The safety factor of 1.5, applied to the Limit Load to derive the Ultimate Load
Ultimate Load Limit Load multiplied by the Factor Of Safety. The Maximum load that the structure must be able to support without failure (for 3 seconds if a static test)
Wing Bending Moment The product of net wing lift and its distance from the measured point.Minimising the wing bending moments is critical in permitting lighter wing and centre wingbox structures. Choice and location of (2,3,4) engines and fuel tanks are critical design considerations that dramatically affect wing bending moments and thus, weight and performance.The A380, LOAD ALLEVIATION Fuel transfer function minimizes wing bending moments by controlling the amount of Outer Wing Tank fuel to:

  • Refueling – ideally no more than 50% full (minimize down moment)
  • Inflight – full (to minimize up moment)

Symbols

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α Alpha Angle of Attack. Incidence
η eta Efficiency
ε Epsilon Downwash Angle
γ gamma Flight path angle to horizontal
ρ rho Density ρ
0 Rho zero Density at sea level
σ sigma Relative density (ρ / ρ0)
θ theta Pitch
Cl Coefficient of lift
Cd Coefficient of drag
G Acceleration
n Load Factor
Q Dynamic Pressure (1/2 ρ V squared) “Q” is used when considering the maximum airframe loads. For example, “Max Q” is called at 35,000’ during every Space Shuttle launch.
S Total wing area (leading and trailing edge surfaces retracted unless specified). Sample wing areas:

  • A380-800 – 845m2
  • B747-400 – 525m2

Weights

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(Bracketed weights are for a typical long haul A380-800 flight Sydney – Los Angeles (6,200 air nm, 12.3 hours, 18t fuel remaining at end of flight)

MEW Manufacturer’s Empty WeightWeight of the aircraft structure, power plant, furnishings, systems and other items of equipment that are considered as part of the manufacturer’s aircraft, MEW includes fluids contained in closed systems (e.g. hydraulic fluid). Does not include the Cabin fitout.
BW MEW plus cabin fitout plus essential basic operational items (unusable fuel, engine oil, emergency equipment, toilet chemicals and fluids, galley structure, seats and documentation, etc.).
OEW Operating Empty Weight.BW plus items plus items specific to the flight (e.g. catering, water, Cabin Crew , miscellaneous). The OEW is not used as an operational weight.
DOW (300t) Dry Operating WeightBW plus any items specific to the flight (e.g. catering (8t), water (2t), tech and cabin crew (2.5t))
Takeoff Fuel (193t or 76% max fuel) Fuel on board at the time of Takeoff.Takeoff Fuel = total fuel loaded minus (taxi fuel (1t) and APU burn (0.4t/hr))
Takeoff Weight (540t or 95% max takeoff weight (MTOW)) The total weight of the aircraft at the commencement of the takeoff roll (brakes released). The aircraft was 1 tonne lighter when lifting off the runway, as the engines had burnt 1 tonne of fuel to accelerate the aircraft to the takeoff speed.ZFW plus takeoff fuel. The TOW must be less than the MTOW.
TTL (66t) Total Traffic Load. Weight of cargo, passengers and passenger baggage.
ZFW (366t) Zero Fuel Weight. DOW plus TTL.
MZFW (366t) Max ZFW. Maximum weight over which all weight must consist of fuel. Its purpose is to limit the maximum load carried in the fuselage.Unlike the other weight limitations, the MZFW is not related to any handling or performance qualities. It is always determined by structural loading and max wing bending moments (when the wing fuel tanks are empty), and is also affected by CG position.An aircraft is most commercially efficient when operating at MZFW (max TTL)Note: the A380-800F freighter, when built, will have a 405t MZFW. This increased weight will most likely be enabled after reinforcement of the wings and wing centre box, fitting of more brakes and perhaps use of more powerful engines
OW Operating Weight. DOW plus fuel on board at takeoff
TOW Takeoff Weight. 
MTOW (569t) Maximum Takeoff Weight. The manufacturers fixed airframe limit further reduced by many tactical operational and environmental limitations (weight, CG, wind, temperature, air pressure, slope, surface strength and condition, brake energy, obstacles, runway length, tire speeds, aircraft serviceability)
Trip Fuel (175t) Fuel used from the commencement of the takeoff until the end of the landing roll
LWT (384t) Landing Weight. Total aircraft weight at landing. Equals TOW minus the Trip Fuel. The LW must be below MLW.
MLW (391t) Maximum Landing Weight. The MLW is reduced, depending on: The manufacturers fixed airframe limit reduced by many tactical operational and environmental limitations: (weight, CG, wing configuration, approach speed increments (for turbulence, icing or aircraft unserviceabilities), wind, temperature, air pressure, slope, surface condition, brake selection, engine reversers, obstacles, runway length, aircraft serviceability)

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