we were departing on AA last Monday and I noticed the AI 747 docked at TBIT was open - but not just the door, a huge section of the fuselage. Upon closer inspection, it appeared that this was the opening to the rear 1/3 of the fuselage which was all cargo - you could see the netting inside. Is this normal for AI to have 747s which are 2/3 pax and 1/3 cargo in the back? Are they the only airline doing this?

Such planes are called combi's. The other airlines I can think of that has 747 combi in service would be Eva Air. I am not too sure, but maybe Asiana also operates such a plane.

Not many operators of the 747-400M these days. Besides EVA, KLM and Asiana are also large operators. Air China also has some.

There are plenty of "747 Combis" around, a number of operators have them although normally only a proportion of their 747 fleet.

Air India have three, their two 747-300s and one 747-400. Normal Air India 747s have a F12 C26 Y385 configuration (yes, only 10% of their seating is premium classes, that's their market), but the Combis are F16 C40 Y227, so only 283 seats instead of 423. There is a rear bulkhead and then a substantial main deck cargo compartment.

Boeing have made 747 Combis for many years, back to the old 747-200. Most people even riding in the aircraft would never notice. It's a substantial structural difference to the mainstream aircraft so normally only incorporated at time of manufacture - there have been just one or two post-modification conversions between the two types.

Different airlines have different approaches to the Combi. For example at KLM the majority of their fleet are of this type. British Airways, operating 747s to pretty much the same places, have none. Similarly, in Korea, Asiana have the majority of their 747 fleet of this type, while Korean Air with many parallel routes have none.

And, there will be even less flying in the future. The new FAA safety regulations, mandating the use of fixed separation walls as opposed to today's movable ones and very stringent fire detection and suppression eqpt standards, have rendered them economically unviable.

Actually, all the AI Combis are in 2-class configuration now. On EPW/EPX, the Business Class is restricted to the Upper Deck only and AIM is in the ex-Air Canada config with Business Class in A-zone and Upper Deck.

LH converted all their 74Ms back to regular config. You can still see where the rear cargo door used to be in some of the old D-ABT.. series aircraft:

http://www.airliners.net/open.file/1060275/L/

On some 747M aircraft, that have less cargo capacity than others, remember there is a movable bulkhead, when there is cargo loaded on the ground crew will put a "pogo stick" on the tail to prevent the plan going nose up!

Alaska Airlines flies a 737-400 combi. The front of the aircraft is cargo and the rear is pax.

They are funky looking
http://www.happiecamper.com/assets/i...lines_2402.jpg