Weight and balance

Light aircraft are pieces of machinery that have limitations, weight and balance in particular. For single or twin-engine aircraft getting the weight and balance right can simply mean the difference between a safe comfortable flight and an unsafe flight. If the weight is wrong, ie overweight, the aircraft will handle like a bag of house bricks, it will require more strip length to takeoff from and land on, the structure of the machine may be comprised, the flight speeds such as the rotation, climb, stall and approach will typically be increased while the cruise speed may be reduced and incur a greater fuel burn to try to obtain the planned flight speed.

Going hand-in-glove with an overweight aircraft is the balance. An aircraft that is overweight will usually, but not always, be beyond the aft centre of gravity (CG) limits and will handle in a manner that the pilot is not expecting. Combined with being overweight an aircraft like this is simply dangerous.

Over the years the ATSB has investigated accidents where the aircraft was found to be both overweight and beyond the CG limits. Those items had been the cause of or have been a major factor in those accidents.

For those who survive flying an overweight and out of balance aircraft having to push the control column forward during the landing, in order to hold up the tail, can be no fun. For many years one central NSW aero club had a photo on its notice board of a six-place single at the fuel station with the tail of the aircraft sitting on the ground. It was an obvious case of being beyond the aft CG with the tail being held up by prop wash but when the engine stopped the tail dropped.

Over the years there have been some memorable scenes when the likes of a few clearly overweight Cherokee Six and Beech A36 aircraft were departing secondary airports for Birdsville or the Bathurst car races. Some of those aircraft almost needed a tailwheel as the tail threatened to contact the ground.

Some aircraft makes and models are known to have potential CG problems unless operated in accordance with the maker’s instructions. Beech singles and twins can have this with fuel being in the leading edge fuel tanks. As fuel is burnt off the CG moves aft and if far enough, control of the aircraft can actually be lost. Aircraft with tip tanks are another example of this potential type of problem. Late model Piper Warriors with the battery on the firewall can have forward CG issues while Piper Seminoles with fullfuel and two robust pilots can also take the CG beyond the forward limits. The Partenavia P-68 can have forward CG issues, sometimes requiring ballast to be carried in the baggage compartment if there are no passengers to trim out the CG. Clearly there are other aircraft makes and models that have the same issues.

Fly per the flight manual limits for safe flight

For new pilots, be they private or commercial pilots and unfamiliar with a new aircraft make or model, it is incumbent on them to become familiar with the weight and balance limits of their mount. At PPL or CPL test time the candidate is usually tested on the weight and balance of the test aircraft with just the two persons on board. It meets the requirements, but when the new licence holder is required to do a gross weight calculation with passengers and baggage they can sometimes be out of their depth to quickly check and calculate that the aircraft is within limits, and will meet the performance requirements.

The simple fix to this is practise. The pilot needs to become familiar with the weight and CG limits of the subject aircraft by calculating a number of samples. Samples of various mixes of people numbers and weight, fuel loads, baggage uplifts and mission profiles. Do not forget to allow for the start and taxi fuel burn off. Passenger weights have to be the actual weight for up to six people on board. Remember also that few aircraft have identical empty weights.

Be prepared for a different empty weight and CG location on every aircraft.

For a new commercial pilot it can pay dividends to know how much the aircraft can legally carry and ensure that it meets the CG limits.

In recent times CASA has been more active in carrying out ramp checks and not just at secondary airports. To have CASA find an aircraft that is overweight and out of CG at some stage of a flight is not conducive to keeping a job or an AOC.

In this day and age of EFBs it does not take long to check the weight numbers and ensure that the aircraft is in CG.

Private or commercial flights, small or large aircraft – they need to be operated within weight and CG limits for well proven handling and safety reasons.