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11.1 Matter, Mass, Weight, Density & Specific Gravity

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FAA Aviation Mechanic — General AMG

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1 Chapter 1: Introduction & AMG Exam Overview

1.1 About the FAA Aviation Mechanic General Knowledge Test 1.2 How to Study for the AMG Exam

2 Chapter 2: Maintenance Forms, Records, Publications & Regulations

2.1 14 CFR Parts 43, 65, and 91 Regulatory Framework 2.2 Aviation Mechanic Privileges, Limitations & Recent Experience 2.3 Maintenance Recordkeeping & Return-to-Service Entries (14 CFR 43.9 & 43.11) 2.4 FAA Form 337 Major Repairs and Major Alterations 2.5 Airworthiness Directives (ADs) & Mandatory Compliance 2.6 Type Certificate Data Sheets (TCDS), STCs, ACs & Maintenance Manuals 2.7 FAA Forms, MMEL/MEL, Inoperative Equipment & Parts Effectivity

3 Chapter 3: Basic Electricity

3.1 DC Electrical Circuits, Ohm's Law & Power 3.2 AC Electrical Fundamentals, Reactance & Impedance 3.3 Aircraft Lead-Acid & Nickel-Cadmium Storage Batteries 3.4 DC Generators, Alternators & Electric Motors 3.5 Aircraft Wiring, Bonding & Circuit Protection Devices 3.6 Resistor Color Codes, Semiconductors, Digital Logic & Electrostatic Discharge

4 Chapter 4: Materials & Processes

4.1 Aircraft Ferrous and Nonferrous Metals & Heat Treatment 4.2 Metal Hardness Testing (Rockwell, Brinell, Vickers) 4.3 Nondestructive Testing (NDT/NDI) Inspection Methods 4.4 Aircraft Hardware, Fasteners & Safetying Methods 4.5 Composite Materials, Plastics & Control Cables 4.6 Soldering, Welding & Weld Quality Inspection

5 Chapter 5: Cleaning & Corrosion Control

5.1 Corrosion Types, Chemistry & Identification 5.2 Corrosion Removal, Chemical Conversion Coatings & Surface Treatments 5.3 Aircraft Cleaning Agents, Precautions & Preventative Maintenance 5.4 Aircraft Finishing Systems, Registration Markings & Placards

6 Chapter 6: Weight & Balance

6.1 Weight and Balance Terminology, Datum, Arm & Moment Principles 6.2 Aircraft Weighing Procedures, Scale Reactions & Tare Weight 6.3 Center of Gravity Computations, Extreme Loading & Ballast

7 Chapter 7: Ground Operation, Servicing & Safety

7.1 Engine Starting Procedures, Danger Areas & Ground Taxi Safety 7.2 Aircraft Servicing (Oxygen, Hydraulic, Pneumatic & De-Icing Fluids) 7.3 Aircraft Fueling Safety, Static Grounding & Hangar Fire Protection 7.4 Airport Movement Areas, Hazardous Materials, Tool Control & FOD Prevention

8 Chapter 8: Aircraft Drawings

8.1 Aircraft Drawing Types, Title Blocks & Orthographic Projections 8.2 Line Conventions, Dimensions, Tolerances & Material Symbols 8.3 Electrical Wiring Diagrams, Logic Flowcharts & Fluid Schematics

9 Chapter 9: Fluid Lines & Fittings

9.1 Rigid Metal Tubing Fabrication, Bending & 37° AN Flaring 9.2 Flexible Hose Construction, Pressure Ratings & Lay Lines 9.3 AN/MS/Quick-Disconnect Fittings, Identification & Installation

10 Chapter 10: Mathematics for Aviation Maintenance

10.1 Fractions, Decimals, Percentages & Ratio/Proportion 10.2 Geometric Computations (Area, Volume & Cylinder Displacement) 10.3 Algebraic Equations, Powers, Roots & Maintenance Conversions

11 Chapter 11: Physics for Aviation Maintenance

11.1 Matter, Mass, Weight, Density & Specific Gravity 11.2 Work, Energy, Power & Simple Machines (Mechanical Advantage) 11.3 Fluid Mechanics, Pascal's Law & Bernoulli's Principle 11.4 Thermodynamics, Heat Transfer, Gas Laws, Sound & Aerodynamics 11.5 Standard Atmosphere, Density & Pressure Altitude, Flight Controls & Aerodynamic Devices

12 Chapter 12: Inspection Concepts, Techniques & Precision Measurement

12.1 Aircraft Inspection Programs & Inspection Concepts 12.2 Precision Measuring Tools & Tool Calibration

13 Chapter 13: Human Factors in Aviation Maintenance

13.1 Human Error, the Dirty Dozen & Maintenance Safety Culture 13.2 Human Performance, Limitations, Fatigue & the Work Environment 13.3 Communication, Shift Turnover, Event Investigation & Professionalism

11.1 Matter, Mass, Weight, Density & Specific Gravity

Key Takeaways Explain This Topic AI

Matter exists in four fundamental physical states—solids, liquids, gases, and plasma—governed by kinetic molecular theory and intermolecular forces including cohesion (attraction between like molecules) and adhesion (attraction between unlike molecules).

Mass ( m m m ) is an invariant measure of matter quantity measured in slugs or kilograms, whereas weight ( W = m × g W = m \times g W = m × g ) is the gravitational force exerted upon that mass measured in pounds force (lbf) or Newtons (N).

Density is mass per unit volume ( ρ = m / V \rho = m/V ρ = m / V ), weight density is weight per unit volume ( D w = W / V D_w = W/V D w ​ = W / V ), and specific volume ( v = 1 / ρ v = 1/\rho v = 1/ ρ ) represents the reciprocal volume occupied per unit mass.

Standard aviation fluid weight densities are: pure water at 62.4 lb/ft 3 62.4\text{ lb/ft}^3 62.4 lb/ft 3 ( 8.34 lb/gal 8.34\text{ lb/gal} 8.34 lb/gal ), 100LL Avgas at 6.0 lb/gal 6.0\text{ lb/gal} 6.0 lb/gal , Jet-A at 6.7 lb/gal 6.7\text{ lb/gal} 6.7 lb/gal , MIL-PRF-5606 at 7.08 lb/gal 7.08\text{ lb/gal} 7.08 lb/gal , Skydrol at 8.93 lb/gal 8.93\text{ lb/gal} 8.93 lb/gal , and dry air at standard sea level at 0.0765 lb/ft 3 0.0765\text{ lb/ft}^3 0.0765 lb/ft 3 .

Hydrometers measure specific gravity via Archimedes' buoyancy principle; lead-acid battery electrolyte hydrometer readings must be corrected for temperature by adding 0.004 0.004 0.004 (+4 points) for each 10 ∘ F 10^\circ\text{F} 1 0 ∘ F above 80 ∘ F 80^\circ\text{F} 8 0 ∘ F and subtracting 0.004 0.004 0.004 (-4 points) for each 10 ∘ F 10^\circ\text{F} 1 0 ∘ F below 80 ∘ F 80^\circ\text{F} 8 0 ∘ F .

Last updated: August 2026

11.1 Matter, Mass, Weight, Density & Specific Gravity

Every aspect of aviation maintenance—from computing aircraft weight and balance to testing lead-acid battery electrolyte, fueling turbine transports, and troubleshooting hydraulic flight controls—relies upon fundamental physics. An Aviation Maintenance Technician (AMT) must possess a thorough understanding of the properties of matter, the critical distinction between mass and weight, fluid densities, and precision specific gravity measurement protocols in accordance with FAA-H-8083-30B (Aviation Maintenance Technician Handbook — General) .

1. Kinetic Molecular Theory & The Four States of Matter

All physical matter occupies space and possesses mass. According to Kinetic Molecular Theory , matter is composed of microscopic atoms and molecules that are in continuous motion. The intensity of molecular motion and the strength of intermolecular attractive forces determine the physical state (phase) of the substance. Four States of Matter Energy Continuum:

  • [ SOLID ] --------> [ LIQUID ] --------> [ GAS ] --------> [ PLASMA ]
  • Definite Shape Indefinite Shape Indefinite Shape Ionized Gas Particles
  • Definite Volume Definite Volume Indefinite Volume Conducts Electricity
  • Low Kinetic Energy Moderate Energy High Energy Extreme High Energy
  • The Four Fundamental States of Matter

Solids: Molecules are held in tightly packed, rigid crystalline or amorphous lattices by powerful intermolecular bonds. Solids maintain a definite shape and definite volume , demonstrating strong resistance to shear, tension, and compression forces (e.g., 2024-T3 aluminum airframe skins, titanium turbine blades).

Liquids: Thermal kinetic energy partially overcomes intermolecular attraction, allowing molecules to slide freely past one another. Liquids possess a definite volume but take the shape of their container . Liquids are practically incompressible, making them ideal for high-pressure hydraulic power transmission (e.g., MIL-PRF-5606 mineral hydraulic fluid, Skydrol phosphate-ester hydraulic fluid).

Gases: Molecular kinetic energy completely overwhelms intermolecular attraction. Gas molecules move independently at high velocity, colliding elastically with one another and container walls. Gases possess neither definite shape nor definite volume , expanding indefinitely to fill any enclosure. Gases are highly compressible, governed by thermodynamic gas laws (e.g., engine bleed air, landing gear oleo strut nitrogen charges).

Plasma: When a gas is subjected to extreme temperatures or high-voltage electromagnetic fields, electrons are stripped from atomic nuclei, creating an ionized gas composed of free electrons and positive ions. Plasma exhibits high electrical conductivity and responds strongly to magnetic fields (e.g., lightning strikes, electrical arcing in high-tension ignition systems, reentry plasma sheaths).

Intermolecular Forces: Cohesion vs. Adhesion

Cohesion: The attractive intermolecular force between like molecules of the same substance. Cohesion gives liquid surfaces surface tension , causing liquid droplets to pull inward into spherical shapes (e.g., mercury forming spherical beads on a flat plate).

Adhesion: The attractive force between unlike molecules of different substances. When adhesion between a liquid and a solid container wall exceeds the internal cohesion of the liquid, the liquid "wets" the surface and climbs upward, forming a concave meniscus (e.g., water in a glass tube). Fluid Meniscus & Intermolecular Forces:

  • Water (Adhesion > Cohesion) Mercury (Cohesion > Adhesion)
  • | | | |
  • | \ / | | /--------\ |
  • | \________/ | | / \ |
  • +----------------+ +----------------+
  • Concave Meniscus Convex Meniscus
  • Capillary Action in Aviation Maintenance

Capillary action is the spontaneous movement of a liquid through narrow passages, crevices, or porous media resulting from the balance of adhesive and cohesive forces, combined with surface tension:

Liquid Penetrant Inspection (NDT): Fluorescent dye penetrants utilize high capillary action to draw low-viscosity penetrant into sub-microscopic surface cracks, fatigue fissures, and porosity defects in turbine blades and structural forgings.

Self-Lubricating Bearings: Porous sintered bronze bushings (Oilite bearings) utilize capillary pores to retain and meter lubricating oil to rotating shafts without requiring external oil lines.

Loading diagram... Intermolecular Forces and Physical State Characteristics

  • 2. Mass, Weight, Density & Specific Volume
  • Mass vs. Weight: Physical Distinction

Many technicians colloquially confuse mass and weight, but their physical definitions and engineering units are distinct:

Mass ( m m m ): The invariant, fundamental measure of the quantity of matter contained within a physical body. Mass represents an object's resistance to acceleration (inertia) and remains identical regardless of gravitational field strength.

English Engineering Unit: Slug ( 1 slug = 32.174 lbf ⋅ s 2 / ft 1\text{ slug} = 32.174\text{ lbf}\cdot\text{s}^2/\text{ft} 1 slug = 32.174 lbf ⋅ s 2 / ft ). A mass of 1 slug accelerates at 1 ft/s 2 1\text{ ft/s}^2 1 ft/s 2 when acted upon by a net force of 1 pound.

SI Metric Unit: Kilogram (kg).

Weight ( W W W ): The downward gravitational force exerted upon a mass by a celestial body (such as Earth). Weight varies in direct linear proportion to local gravitational acceleration ( g g g ): W = m × g W = m \times g W = m × g

Where g = 32.174 ft/s 2 g = 32.174\text{ ft/s}^2 g = 32.174 ft/s 2 (standard Earth gravity at sea level) or 9.807 m/s 2 9.807\text{ m/s}^2 9.807 m/s 2 .

English Engineering Unit: Pound force (lbf or lb) .

SI Metric Unit: Newton (N) ( 1 N = 1 kg ⋅ m/s 2 1\text{ N} = 1\text{ kg}\cdot\text{m/s}^2 1 N = 1 kg ⋅ m/s 2 ). Mass in Slugs = Weight in Pounds ( W ) g ( 32.2 ft/s 2 ) \text{Mass in Slugs} = \frac{\text{Weight in Pounds } (W)}{g \; (32.2\text{ ft/s}^2)} Mass in Slugs = g ( 32.2 ft/s 2 ) Weight in Pounds ( W ) ​

Aviation Acceleration Note: When an aircraft executes a 3.0 G 3.0\text{ G} 3.0 G coordinated pullout, an avionics component with a mass of 2.0 slugs 2.0\text{ slugs} 2.0 slugs ( W = 64.4 lbs W = 64.4\text{ lbs} W = 64.4 lbs at 1.0 G 1.0\text{ G} 1.0 G ) experiences an effective gravitational acceleration of 3.0 × 32.2 ft/s 2 = 96.6 ft/s 2 3.0 \times 32.2\text{ ft/s}^2 = 96.6\text{ ft/s}^2 3.0 × 32.2 ft/s 2 = 96.6 ft/s 2 . Its mass remains strictly 2.0 slugs 2.0\text{ slugs} 2.0 slugs , while its apparent weight surges to 193.2 lbs 193.2\text{ lbs} 193.2 lbs .

Density ( ρ \rho ρ ), Weight Density ( D w D_w D w ​ ), and Specific Volume ( v v v )

Mass Density ( ρ \rho ρ ): Mass per unit volume of a substance: ρ = Mass ( m ) Volume ( V ) [ slugs ft 3 or kg m 3 ] \rho = \frac{\text{Mass } (m)}{\text{Volume } (V)} \qquad \left[\frac{\text{slugs}}{\text{ft}^3} \text{ or } \frac{\text{kg}}{\text{m}^3}\right] ρ = Volume ( V ) Mass ( m ) ​ [ ft 3 slugs ​ or m 3 kg ​ ]

Weight Density ( D w D_w D w ​ ): Weight force per unit volume of a substance: D w = Weight ( W ) Volume ( V ) = ρ × g [ lb ft 3 , lb in 3 , or lb U.S. gal ] D_w = \frac{\text{Weight } (W)}{\text{Volume } (V)} = \rho \times g \qquad \left[\frac{\text{lb}}{\text{ft}^3}, \; \frac{\text{lb}}{\text{in}^3}, \text{ or } \frac{\text{lb}}{\text{U.S. gal}}\right] D w ​ = Volume ( V ) Weight ( W ) ​ = ρ × g [ ft 3 lb ​ , in 3 lb ​ , or U.S. gal lb ​ ]

Specific Volume ( v v v ): The volume occupied per unit mass or unit weight of a substance, representing the mathematical reciprocal of density: v = V m = 1 ρ [ ft 3 slug , ft 3 lb , or m 3 kg ] v = \frac{V}{m} = \frac{1}{\rho} \qquad \left[\frac{\text{ft}^3}{\text{slug}}, \; \frac{\text{ft}^3}{\text{lb}}, \text{ or } \frac{\text{m}^3}{\text{kg}}\right] v = m V ​ = ρ 1 ​ [ slug ft 3 ​ , lb ft 3 ​ , or kg m 3 ​ ]

As a gas is heated at constant pressure, its volume expands, causing its density to decrease and its specific volume to increase.

Standard Aviation Fluid Densities and Weights

AMTs must know standard fluid weights by memory for aircraft fueling, weight and balance calculations, and fluid service checks:

Aviation Fluid Weight Density ( lb/gal \text{lb/gal} lb/gal ) Weight Density ( lb/ft 3 \text{lb/ft}^3 lb/ft 3 ) Specific Gravity ( S G SG SG ) Aviation Application & Notes

Pure Water ( 4 ∘ C 4^\circ\text{C} 4 ∘ C ) 8.34 lb/gal 8.34\text{ lb/gal} 8.34 lb/gal 62.4 lb/ft 3 62.4\text{ lb/ft}^3 62.4 lb/ft 3 1.000 1.000 1.000 Universal reference baseline for liquid specific gravity.

Aviation Gasoline (100LL Avgas) 6.00 lb/gal 6.00\text{ lb/gal} 6.00 lb/gal 44.88 lb/ft 3 44.88\text{ lb/ft}^3 44.88 lb/ft 3 0.720 0.720 0.720 Piston engine fuel (Blue dye; low density hydrocarbons).

Aviation Turbine Fuel (Jet-A / Jet-A-1) 6.70 lb/gal 6.70\text{ lb/gal} 6.70 lb/gal 50.12 lb/ft 3 50.12\text{ lb/ft}^3 50.12 lb/ft 3 0.803 0.803 0.803 Kerosene-grade turbine fuel (Straw color; heavier than Avgas).

MIL-PRF-5606 Hydraulic Fluid 7.08 lb/gal 7.08\text{ lb/gal} 7.08 lb/gal 52.96 lb/ft 3 52.96\text{ lb/ft}^3 52.96 lb/ft 3 0.849 0.849 0.849 Mineral-base hydraulic fluid (Red dye; general aviation standard).

Phosphate-Ester Fluid (Skydrol LD-4) 8.93 lb/gal 8.93\text{ lb/gal} 8.93 lb/gal 66.80 lb/ft 3 66.80\text{ lb/ft}^3 66.80 lb/ft 3 1.071 1.071 1.071 Synthetic fire-resistant fluid (Purple/Green; heavier than water).

Aircraft Engine Oil (SAE 50 / Grade 100) 7.50 lb/gal 7.50\text{ lb/gal} 7.50 lb/gal 56.10 lb/ft 3 56.10\text{ lb/ft}^3 56.10 lb/ft 3 0.899 0.899 0.899 Piston engine mineral reciprocating lubricating oil.

Dry Air (Standard Sea Level, 15 ∘ C 15^\circ\text{C} 1 5 ∘ C ) — 0.0765 lb/ft 3 0.0765\text{ lb/ft}^3 0.0765 lb/ft 3 1.000 1.000 1.000 (Gas Ref) 1.225 kg/m 3 1.225\text{ kg/m}^3 1.225 kg/m 3 ; universal reference standard for gas S G SG SG .

  • 3. Specific Gravity ( S G SG SG ) & Hydrometer Principles
  • Definition of Specific Gravity

Specific Gravity ( S G SG SG ) is a dimensionless ratio comparing the density of a given substance to the density of a standard reference substance at a specified temperature:

For Liquids and Solids: The standard reference is pure distilled water at 4 ∘ C 4^\circ\text{C} 4 ∘ C ( 39.2 ∘ F 39.2^\circ\text{F} 39. 2 ∘ F ) , where water attains its maximum density of 1.000 g/cm 3 1.000\text{ g/cm}^3 1.000 g/cm 3 , 1 , 000 kg/m 3 1,000\text{ kg/m}^3 1 , 000 kg/m 3 , 62.4 lb/ft 3 62.4\text{ lb/ft}^3 62.4 lb/ft 3 , or 8.34 lb/U.S. gal 8.34\text{ lb/U.S. gal} 8.34 lb/U.S. gal : S G liquid = Density of Liquid Density of Pure Water at 4 ∘ C = D w , liquid 8.34 lb/gal SG_{\text{liquid}} = \frac{\text{Density of Liquid}}{\text{Density of Pure Water at } 4^\circ\text{C}} = \frac{D_{w\text{, liquid}}}{8.34\text{ lb/gal}} S G liquid ​ = Density of Pure Water at 4 ∘ C Density of Liquid ​ = 8.34 lb/gal D w , liquid ​ ​

For Gases: The standard reference is dry air at Standard Sea Level conditions ( 15 ∘ C / 59 ∘ F 15^\circ\text{C} / 59^\circ\text{F} 1 5 ∘ C /5 9 ∘ F and 29.92 inHg / 1013.25 hPa 29.92\text{ inHg} / 1013.25\text{ hPa} 29.92 inHg /1013.25 hPa ), possessing a density of 0.0765 lb/ft 3 0.0765\text{ lb/ft}^3 0.0765 lb/ft 3 ( 1.225 kg/m 3 1.225\text{ kg/m}^3 1.225 kg/m 3 ): S G gas = Density of Gas Density of Dry Air at Standard Sea Level = ρ gas 0.0765 lb/ft 3 SG_{\text{gas}} = \frac{\text{Density of Gas}}{\text{Density of Dry Air at Standard Sea Level}} = \frac{\rho_{\text{gas}}}{0.0765\text{ lb/ft}^3} S G gas ​ = Density of Dry Air at Standard Sea Level Density of Gas ​ = 0.0765 lb/ft 3 ρ gas ​ ​

Hydrometer Operation & Archimedes' Principle

A hydrometer is a sealed, hollow glass instrument containing a weighted bulb at the bottom and a graduated stem at the top. It measures liquid specific gravity based on Archimedes' Buoyancy Principle :

A floating body displaces a weight of fluid exactly equal to the total weight of the floating body.

In Low-Density Liquids ( S G < 1.0 SG < 1.0 SG < 1.0 , e.g., Gasoline 0.72 0.72 0.72 ): The hydrometer must submerge deeply to displace enough fluid mass to equal its own weight, causing the liquid meniscus to read low on the upper stem scale.

In High-Density Liquids ( S G > 1.2 SG > 1.2 SG > 1.2 , e.g., Battery Acid 1.28 1.28 1.28 ): The dense fluid provides greater upward buoyant force per unit depth, floating the hydrometer high out of the liquid and exposing more of the graduated stem.

Loading diagram... Hydrometer Floating Equilibrium in Battery Electrolyte

4. Lead-Acid Battery Electrolyte Testing & Temperature Correction

Aircraft lead-acid storage batteries utilize an electrolyte consisting of approximately 27% sulfuric acid ( H 2 S O 4 H_2SO_4 H 2 ​ S O 4 ​ ) and 73% distilled water by weight. As the battery discharges, sulfate ions ( S O 4 2 − SO_4^{2-} S O 4 2 − ​ ) leave the electrolyte and chemically bind to the lead plates as lead sulfate ( P b S O 4 PbSO_4 P b S O 4 ​ ), leaving water behind and lowering electrolyte specific gravity .

State of Charge vs. Specific Gravity Scale ( 80 ∘ F 80^\circ\text{F} 8 0 ∘ F Base)

State of Charge Specific Gravity ( 80 ∘ F 80^\circ\text{F} 8 0 ∘ F ) Electrolyte Condition & AMT Action

100% Fully Charged 1.275 − 1.300 1.275 - 1.300 1.275 − 1.300 Battery in optimal state; ready for airframe installation.

75% Charged 1.240 − 1.270 1.240 - 1.270 1.240 − 1.270 Operational; normal in-service range.

50% Charged 1.200 − 1.240 1.200 - 1.240 1.200 − 1.240 Battery requires bench recharge before flight dispatch.

Discharged / Dead < 1.150 < 1.150 < 1.150 High water content; susceptible to plate sulfation and cell freezing.

The Standard Temperature Correction Formula

Hydrometers are calibrated at a reference standard temperature of 80 ∘ F 80^\circ\text{F} 8 0 ∘ F ( 26.7 ∘ C 26.7^\circ\text{C} 26. 7 ∘ C ) . Because liquids expand when heated (reducing observed density) and contract when cooled (increasing observed density), observed hydrometer readings taken at temperatures other than 80 ∘ F 80^\circ\text{F} 8 0 ∘ F must be mathematically corrected: True Corrected S G = Observed S G ± ( T actual − 80 ∘ F 10 ∘ F × 0.004 ) \text{True Corrected } SG = \text{Observed } SG \pm \left(\frac{T_{\text{actual}} - 80^\circ\text{F}}{10^\circ\text{F}} \times 0.004\right) True Corrected SG = Observed SG ± ( 1 0 ∘ F T actual ​ − 8 0 ∘ F ​ × 0.004 ) { Above 80 ∘ F : ADD 0.004 (4 points) for every 10 ∘ F Above 80 ∘ F Below 80 ∘ F : SUBTRACT 0.004 (4 points) for every 10 ∘ F Below 80 ∘ F \begin{cases} \mathbf{\text{Above } 80^\circ\text{F}:} & \mathbf{\text{ADD } 0.004 \text{ (4 points) for every } 10^\circ\text{F Above } 80^\circ\text{F}} \\ \mathbf{\text{Below } 80^\circ\text{F}:} & \mathbf{\text{SUBTRACT } 0.004 \text{ (4 points) for every } 10^\circ\text{F Below } 80^\circ\text{F}} \end{cases} { Above 8 0 ∘ F : Below 8 0 ∘ F : ​ ADD 0.004 (4 points) for every 1 0 ∘ F Above 8 0 ∘ F SUBTRACT 0.004 (4 points) for every 1 0 ∘ F Below 8 0 ∘ F ​ Temperature Correction Rule of Thumb:

  • Temp > 80°F ---> Electrolyte expanded (reads false LOW) ---> ADD correction
  • Temp < 80°F ---> Electrolyte contracted (reads false HIGH) ---> SUBTRACT correction
  • 5. Worked Calculation Examples
  • Example 1: Aircraft Fuel Weight and Loading Comparison

Problem: A flight operations coordinator must load 120 U.S. gallons of fuel into an aircraft. The aircraft was mistakenly fueled with 120 gallons of Jet-A instead of 120 gallons of 100LL Avgas.

Compute the fuel weight for both fuels and determine the excess weight added to the airframe.

Solution:

Calculate weight of 120 gallons of 100LL Avgas ( D w = 6.0 lb/gal D_w = 6.0\text{ lb/gal} D w ​ = 6.0 lb/gal ): W Avgas = 120 gal × 6.0 lb/gal = 720.0 lbs W_{\text{Avgas}} = 120\text{ gal} \times 6.0\text{ lb/gal} = 720.0\text{ lbs} W Avgas ​ = 120 gal × 6.0 lb/gal = 720.0 lbs

Calculate weight of 120 gallons of Jet-A ( D w = 6.7 lb/gal D_w = 6.7\text{ lb/gal} D w ​ = 6.7 lb/gal ): W Jet-A = 120 gal × 6.7 lb/gal = 804.0 lbs W_{\text{Jet-A}} = 120\text{ gal} \times 6.7\text{ lb/gal} = 804.0\text{ lbs} W Jet-A ​ = 120 gal × 6.7 lb/gal = 804.0 lbs

Calculate excess weight added: Δ W = 804.0 lbs − 720.0 lbs = 84.0 lbs \Delta W = 804.0\text{ lbs} - 720.0\text{ lbs} = 84.0\text{ lbs} Δ W = 804.0 lbs − 720.0 lbs = 84.0 lbs

(Note: Misfueling reciprocating engines with Jet-A also causes catastrophic detonation and engine destruction).

Example 2: Hydrometer Temperature Correction Under High Heat

Problem: A technician tests an aircraft battery in a hangar where ambient temperature is 110 ∘ F 110^\circ\text{F} 11 0 ∘ F . The hydrometer float indicates an observed specific gravity of 1.275 1.275 1.275 .

Determine the true corrected specific gravity of the battery cell.

Solution:

Determine temperature difference from 80 ∘ F 80^\circ\text{F} 8 0 ∘ F reference: Δ T = 110 ∘ F − 80 ∘ F = + 30 ∘ F ( three 10 ∘ F increments above baseline ) \Delta T = 110^\circ\text{F} - 80^\circ\text{F} = +30^\circ\text{F} \quad (\text{three } 10^\circ\text{F increments above baseline}) Δ T = 11 0 ∘ F − 8 0 ∘ F = + 3 0 ∘ F ( three 1 0 ∘ F increments above baseline )

Calculate correction factor: Correction = + 30 ∘ F 10 ∘ F × ( + 0.004 ) = 3 × ( + 0.004 ) = + 0.012 \text{Correction} = \frac{+30^\circ\text{F}}{10^\circ\text{F}} \times (+0.004) = 3 \times (+0.004) = +0.012 Correction = 1 0 ∘ F + 3 0 ∘ F ​ × ( + 0.004 ) = 3 × ( + 0.004 ) = + 0.012

Calculate true corrected specific gravity: Corrected S G = 1.275 + 0.012 = 1.287 \text{Corrected } SG = 1.275 + 0.012 = 1.287 Corrected SG = 1.275 + 0.012 = 1.287

(Conclusion: The battery is in a fully charged state ( > 1.275 >1.275 > 1.275 )).

Example 3: Hydrometer Temperature Correction Under Sub-Freezing Conditions

Problem: During winter line operations at 20 ∘ F 20^\circ\text{F} 2 0 ∘ F , a battery hydrometer indicates an observed reading of 1.265 1.265 1.265 .

Determine the true corrected specific gravity.

Solution:

Determine temperature difference from baseline: Δ T = 20 ∘ F − 80 ∘ F = − 60 ∘ F ( six 10 ∘ F increments below baseline ) \Delta T = 20^\circ\text{F} - 80^\circ\text{F} = -60^\circ\text{F} \quad (\text{six } 10^\circ\text{F increments below baseline}) Δ T = 2 0 ∘ F − 8 0 ∘ F = − 6 0 ∘ F ( six 1 0 ∘ F increments below baseline )

Calculate correction factor: Correction = − 60 ∘ F 10 ∘ F × ( 0.004 ) = 6 × ( − 0.004 ) = − 0.024 \text{Correction} = \frac{-60^\circ\text{F}}{10^\circ\text{F}} \times (0.004) = 6 \times (-0.004) = -0.024 Correction = 1 0 ∘ F − 6 0 ∘ F ​ × ( 0.004 ) = 6 × ( − 0.004 ) = − 0.024

Calculate true corrected specific gravity: Corrected S G = 1.265 − 0.024 = 1.241 \text{Corrected } SG = 1.265 - 0.024 = 1.241 Corrected SG = 1.265 − 0.024 = 1.241

(Conclusion: The cell is only ~70% charged and requires shop recharging before flight dispatch).