747-400M (Combi)

The 747-400M is the last and most numerous 747 Combi — 61 built — and the final expression of an idea that had been in the family since 1975: carry passengers and freight on the same main deck, and change the split whenever the market does.

How it works

A large side cargo door sits behind the left wing. Passenger seats in the rear main deck can be removed and cargo tracks installed, letting the airline carry containers or pallets on the main deck behind the passenger cabin. A locked partition separates the two, accessible only by the crew.

Roller trays in the aft floor take 8-foot-wide containers or pallets up to 20 feet long — any container or pallet in standard aviation use.

The turnaround trick

The Combi’s cleverest feature is one almost nobody notices: it can be turned round in the same time as an ordinary passenger 747.

Main-deck cargo loading happens aft, in a part of the aircraft where nothing else is going on, while passengers board through the forward doors. The two operations do not interfere with each other at all.

That works because of the 747’s landing gear layout. The fore-and-aft arrangement of the wing and body gear gives enough stability to load heavy freight into the rear fuselage without the aircraft sitting back on its tail — something a conventionally geared aircraft could not do safely.

What it carried

The list is unusual for a passenger aircraft: automobiles, small boats, heavy machinery, drilling equipment, and small aircraft and helicopters. Environmental control in the cargo area allowed live animals, perishable food and cut flowers, with the passenger cabin conditioned separately.

Improvements over earlier Combis

The -400M added extra fire protection, the two-crew digital flight deck of the 747-400, advanced engines, wingtip extensions with winglets and new interiors.

The fire protection was not incidental. Main-deck cargo on a Combi sits on the same deck as passengers, and after the loss of a South African Airways 747-200M to an in-flight cargo fire in 1987, the standards applied to those compartments were tightened substantially.

The stretched upper deck also matters here more than on a normal airliner: on the -300 and -400 Combis it accommodates 44 more passengers than the standard 747-200 Combi, recovering upstairs some of the main-deck seating given over to freight.

KLM was the launch customer and the archetypal operator. Across the whole family, more than 30 customers flew a total of 144 747 Combis, 58 of them -400s.

Why it ended

Two forces closed the configuration down. Compliance costs for main-deck fire suppression rose, and the economics of splitting an aircraft between two jobs stopped competing with running dedicated freighters alongside dedicated passenger aircraft.

The last passenger-carrying 747 Combis left service in the 2010s. Note also that the 747-400C does not exist — the “C” is a common mix-up with this aircraft’s “M”.