Weight limits: MTOW, landing, and structure
Each weight limit protects something different, including structure, not just CG or performance.
Published limits:
| Limit | Meaning | Detail |
|---|---|---|
| Max landing weight | Greatest weight normally allowed at touchdown | Some types set it below MTOW to cap arrival gear and structural loads; many light singles publish same figure for both |
| Max zero-fuel weight (ZFW) | Max weight excluding usable fuel (PHAK) | Weight without usable fuel must not exceed max ZFW (TP 13723, weight and balance assessment); if over, cut passengers or cargo, not fuel (PHAK ch.10) |
Why weight limits exist (TP 1102):
- Weight distribution: effect on stall/spin and stability.
- Weight: effect on primary and secondary structure.
- Weight: effect on takeoff and landing performance.
Overloading effects (beyond takeoff/landing performance):
- Climb and cruise: overheating in climbs, added engine wear, higher fuel consumption, reduced range (TP 1102, Aircraft Weight); slower cruise (PHAK).
- Climb: weight's effect on performance more pronounced than in any other normal manoeuvre (TP 1102 Ex.7 Climbing).
- Ground effect: max-gross-weight aircraft can leave ground in acceptable distance; once out of it, rate of climb may be seriously affected (TP 1102 Ex.7 Climbing).
- Habitual overloading: cumulative structural stress and damage preflight inspection may not catch; can cause later structural failure in completely normal operations; believed to accelerate metal fatigue failures (PHAK).
- Stability: aircraft stable and controllable normally loaded can behave very differently overloaded; greater gross weight expected to hurt stability regardless of CG position (PHAK).
Trap: treating MTOW as the only number that matters; landing weight governs at touchdown.
References
- TP 1102 ch.2, Weight and Balance
- TP 1102 Ex.7 Climbing
- PHAK ch.5, Aerodynamics of Flight (Effect of Weight on Aircraft Structure; Effect of Weight on Flight Performance)
- PHAK ch.10, Weight and Balance (glossary)
- TP 1102, Aircraft Weight
- TP 13723 PPL Flight Test Guide, weight and balance assessment