Weight, Balance, and Loading

No — the concept is no different than that of a single-engine airplane. The execution, however, is almost invariably more complex (AFH ch. 13).

The new loading areas: nose and aft baggage compartments, nacelle lockers, main fuel tanks, auxiliary fuel tanks, nacelle fuel tanks, and numerous seating options across a variety of interior configurations. That flexibility places a responsibility on the pilot to address weight and balance prior to each flight.

standard empty weight + optional equipment = basic empty weight — GAMA's standardized terms, adopted in 1975 and implemented by most manufacturers starting model year 1976 (AFH ch. 13):

• Standard empty weight — the standard airplane, full hydraulic fluid, unusable fuel, and full oil
• Optional equipment — the weight of all equipment installed beyond standard
• Basic empty weight — standard empty weight plus optional equipment. Includes no usable fuel, but full oil

Pre-GAMA airplanes generally use (AFH ch. 13):

empty weight + unusable fuel = standard empty weight

standard empty weight + optional equipment = licensed empty weight

Here empty weight is the standard airplane, full hydraulic fluid, and undrainable oil.

The major difference between the two formats: basic empty weight includes full oil and licensed empty weight does not. Oil should always be added to any weight and balance utilizing a licensed empty weight.

Because when the airplane is placed in service, amended documents are prepared by rated maintenance personnel to reflect equipment changes — and maintenance personnel are under no regulatory obligation to utilize the GAMA terminology (AFH ch. 13).

Superseded documents are customarily marked "superseded" and retained in the AFM/POH. Use care to determine whether oil has to be added to the calculation or is already included.

The maximum allowable weight of the airplane and payload, assuming there is no usable fuel on board (AFH ch. 13). The actual airplane isn't devoid of fuel at loading, of course — it's a calculation that assumes it was.

If a zero fuel weight limitation is published, then all weight in excess of that figure should consist of usable fuel.

Its purpose: to limit load forces on the wing spars with heavy fuselage loads. Fuel in the wings relieves those forces; payload in the fuselage adds to them. Not all multiengine airplanes publish a zero fuel weight, but many do — the twin is where most pilots meet the term for the first time.

• Useful load — the maximum combination of usable fuel, passengers, baggage, and cargo the airplane can carry. Maximum takeoff weight minus basic empty weight
• Payload — the maximum combination of passengers, baggage, and cargo the airplane can carry. A zero fuel weight, if published, is the limiting weight

(AFH ch. 13)

• Ramp weight — a weight in excess of maximum takeoff weight, allowing for fuel burned during taxi and run-up so a takeoff can be made at full maximum takeoff weight. The airplane should weigh no more than maximum takeoff weight at the beginning of the takeoff roll
• Maximum landing weight — a limitation against landing above the published value. This requires preflight planning of fuel burn to ensure arrival weight is at or below it

(AFH ch. 13)

Land — but understand what you're spending. The structural margins designed into the airplane are not fully available when over landing weight. An overweight landing inspection may be advisable; consult the service manual or the manufacturer (AFH ch. 13).

The flight characteristics of a multiengine airplane vary significantly with shifts of the CG within the approved envelope (AFH ch. 13):

Forward CG — more stable, slightly higher stalling speed, slightly slower cruising speed, favorable stall characteristics

Aft CG — less stable, slightly lower stalling speed, slightly faster cruising speed, less desirable stall characteristics

Forward CG limits are usually determined in certification by elevator/stabilator authority in the landing round out. Aft CG limits are determined by the minimum acceptable longitudinal stability.

VMC increases as the CG is moved aft. The moment arm of the rudder is reduced, and therefore its effectivity is reduced, as the CG moves aft. For a typical light twin, the aft-most CG limit is the most unfavorable CG position (AFH ch. 13, 23.149(b)).

This is why VMC is certificated at the most unfavorable CG — and why an aft-loaded airplane has a higher actual red line than the one painted on the ASI.

VMC increases as weight is reduced (AFH ch. 13).

It is emphatically not good news, because the same lighter weight that raises VMC also improves single-engine climb. Light training twins can therefore have deceptively good single-engine performance combined with a higher actual VMC — the AFH notes most multiengine training is conducted in four-to-six place airplanes at weights significantly below maximum, where single-engine performance, particularly at low density altitudes, may be deceptively good.

Yes. Some multiengine airplanes require ballast to remain within CG limits under certain loading conditions (AFH ch. 13):

• Several models require ballast in the aft baggage compartment with only a learner and instructor on board, to avoid exceeding the forward CG limit
• When passengers occupy the aft-most seats of some models, ballast or baggage may be required in the nose baggage compartment to avoid exceeding the aft CG limit

When ballast is added, it must be securely tied down and must not exceed the maximum allowable floor loading.

No — it is contrary to the airplane's operating limitations and to 14 CFR to exceed any weight and balance parameter (AFH ch. 13). It's a regulatory violation, not a judgment call.

Work it from the handbook's own figures rather than memorizing a constant: 800 lb of fuel is stated as 133.3 gallons, and 180 gallons is stated as 1,080 lb (AFH ch. 13). Both give 6 lb per gallon for avgas.

Always use the weight per gallon your AFM/POH specifies for the fuel grade you're actually carrying.

Nose baggage compartment, aft baggage compartment, nacelle lockers, main fuel tanks, auxiliary fuel tanks, and nacelle fuel tanks — plus many seating configurations (AFH ch. 13).

Each is a separate arm on the loading form, and the nose and nacelle stations sit at very different moment arms from anything on a single-engine trainer. The nose compartment in particular can swing the CG forward hard, which is exactly why some models use it as ballast for aft-loaded passengers.

Two, and both have killed people (AFH ch. 13):

1. Security of the latches and locks. When improperly secured the door may open and contents may be drawn out — usually into the propeller arc, and usually just after takeoff. Even when empty, airplanes have been lost when the pilot became distracted by the open door
2. Inspection of the interior. More than one pilot has been surprised to find a supposedly empty compartment packed to capacity or loaded with ballast. Tow bars, inlet covers, sun screens, oil containers, spare chocks, and hand tools must be secured to prevent damage from shifting in flight

A device with several movable parts adjusted over a plotting board on which the CG envelope is printed. A pencil line plot can be made directly on the envelope, erased, and recalculated for each flight. The reverse side typically contains general loading recommendations for that airplane (AFH ch. 13).

It is to be used only for the make and model airplane for which it was designed.

From the certification conditions and performance discussion (AFH ch. 13):

The uncomfortable conclusion: there is no loading that optimizes both. A light, aft-loaded training twin has good single-engine climb and a raised actual VMC. A heavy twin has a lower actual VMC and may have no single-engine climb at all.

Forward CG has one clear safety benefit worth naming: flying with a CG closer to the forward limit provides better stall and spin avoidance characteristics — though the AFH is careful to add that it does not eliminate the hazard (AFH ch. 13).

Because the majority of multiengine training is conducted in four-to-six place airplanes at weights significantly less than maximum, where single-engine performance — particularly at low density altitudes — may be deceptively good (AFH ch. 13).

To show the performance you'd actually see at higher weights, altitudes, and temperatures, an instructor may artificially limit the manifold pressure available on the operative engine; airport operations above the single-engine ceiling can be simulated the same way.

What an instructor should not do: load the airplane with passengers to practice emergencies at maximum takeoff weight — the AFH calls that an unnecessary training hazard.

As the first of the AFH's takeoff planning factors: weight and balance, airplane performance (both single- and multiengine), runway length, slope and contamination, terrain and obstacles, weather conditions, and pilot proficiency (AFH ch. 13).

Prior to takeoff, ensure that weight and balance limitations have been observed, the runway length is adequate, and the normal flightpath clears obstacles and terrain — then decide what you'll do if an engine quits at any point during the takeoff.