I am with WHBM on this, Boeing seem to have lost their way a little over the last ten years or so. They have "tweaked" a number of airframes which haven't proven commercial successes (B753, B764, & B736) and so far the B748 is looking doubtful, certainly in the passenger version. Similarly they have been distracted by things like the "Sonic Cruiser". In their defence the B777 is in a league of it's own and has probably contributed to the demise of the B747 passenger series as well as the B767-400.
The B737NG is selling well but one has to wonder at what price?
Can you be more specific on where the 737-900 starts to lose its touch? It seems to be getting the 737 more up to 707-type fuselage size. I'm interesting in understanding where it fails.
Again I would contend that Boeing took their eye off the ball here. The aircraft is supposed to compete with the Airbus A321, carrying c210 passengers on up to c2000+nm legs. However the B737-900 can only carry 189 pax due to the fact that the emergency exits don't meet present passenger evacuation requirements. To fix this Boeing have come up with the -ER version where they have had to install a pair of emergency exit doors (D doors?) behind the wing in addition to the normal pair of overwing exits.
JetPhotos.Net Photo » PK-LFG (CN: 35680) Lion Air Boeing 737-9GPER by NGO Spotter By doing so they effectively lost a row of seats and so they had to re-design the rear pressure bulkhead, and make it flat, redesign the rear galley and toilets all so they could recover the "lost" row of seats, and presumably the empty weight went up too!
However back to the basic B737-900, we now have a 189 seat aeroplane which can only legally carry the same number of passengers as the B737-800 but of course the airframe weighs a couple of thousand pounds more. I fly the -900 with 24K engines and 188 passengers, and I used to fly the A321 with 215 passengers. In a straight head to head with the A321 with a full passenger load on a similar 4-5 Hr flight. They will both climb initially to approx. FL330-340. There the A321 will cruise at approx. M.79 whereas the B739 will be M.78 or less. The B739 will be burning about 3100-3200 lbs per hour for the first couple of hours, which if memory serves is similar to the A321 with V2500s. Granted the B739 will climb higher sooner than the A321, but it doesn't disguise the fact that it is slower than the A321, and carries less passengers. Basically it's not doing anything that the slightly smaller B737-800 isn't already doing, something the world's airlines have recognised and sales of the B737-900 have not been fantastic.
Now don't get me started on the shortfalls of the -NG series generally.
