Centre of Gravity, Moments and Load Sheets
Datum, arm, moment, index, percent MAC, load-and-trim sheets and the effect of loading changes.
How to prepare for UK CAA ATPL theory
Work from your ATO recommendation and selected A/H route, master the official learning objectives by subject code, then rehearse paper-specific timing, calculations and operational decisions.
Core concepts
Concept 1
Centre of gravity is found by dividing total moment by total mass using a consistent datum, sign convention and unit system.
Exam cue: Write the datum and sign convention before entering arms and moments.
Concept 2
Index systems and percent MAC scale or re-express the same mass-and-moment relationship.
Exam cue: Check whether a table uses raw moment, moment divided by a factor or an index.
Concept 3
Adding, removing or moving mass shifts the centre of gravity according to the mass and distance involved.
Exam cue: Predict the direction of CG movement before calculating its size.
Risk pitfalls and guardrails
Mixing mass, weight, arm and moment units.
Guardrail: Do not mix ATPL(A), ATPL(H) and ATPL(H)/IR paper requirements or treat the aggregate 601-item study allocation as an official CAA examination total.
Dropping an index scaling factor.
Guardrail: Do not mix ATPL(A), ATPL(H) and ATPL(H)/IR paper requirements or treat the aggregate 601-item study allocation as an official CAA examination total.
Moving the CG in the wrong direction after a load shift.
Guardrail: Do not mix ATPL(A), ATPL(H) and ATPL(H)/IR paper requirements or treat the aggregate 601-item study allocation as an official CAA examination total.
Memory anchors
Moment
Moment equals mass multiplied by arm.
CG
Centre-of-gravity arm equals total moment divided by total mass.
Shift Direction
The CG moves toward added mass and toward the new position of moved mass.
Percent MAC
Percent MAC expresses CG position relative to the leading edge and length of the mean aerodynamic chord.
Sense Check
Predict forward or aft movement first, then verify the numerical result lies inside the envelope.
Checkpoint rule
Do the check-up only after you can summarize each concept in one sentence and identify one dangerous pitfall from memory.
Knowledge Check (after reading)
Short check-up to confirm understanding of this module.
Check-up Questions
An aircraft mass is 8,000 kg with total moment 19,200 kg·m. Where is the CG from the datum?
A 600 kg item at arm 4.0 m is added to an aircraft of 4,400 kg at CG arm 2.5 m. What is the new CG arm?
Answer all questions to submit.
Next step personalized recommendations
Continue learning
Move forward only after this module is stable.
What is Pass Harbor?
Completely free exam prep for 247 UK exams.
- Practice questions
- Flashcards
- Study guides
- Mock exams
- No registration
- No paywall
- Start instantly
“No more expensive exam prep. Quality study tools should be accessible to everyone.”