why aren't there three engine airliners?
 

727s, L-1011s and DC-10/MD-11s are out of service as airliners. Are there flaws inherent to the three engine concept or did the executions just not have staying power?

Sixto
87 300D

KLM still operates the MD-11, so the tri-jets aren't entirely gone from the passenger jet scene. 727s and DC-10s can still be found doing cargo duty, but L-1011s are just about all relegated to the private and military scene now.

Since the 60s and 70s when those aircraft were designed and introduced, jet engines have become more fuel efficient and more powerful. Thus, the need for 3 engines dropped when the same flights could be accomplished with 2 engines with less fuel burn to boot. There was also one less engine to maintain and you know how airlines like to save money.

Just take a look at what 2 engined jets those tri-jets have been typically replaced with.

727= 737-800/900, 757-200, A320/321
L-1011= 767-400, 777-200, A330
DC-10/MD-11= 767-400, 777-200, A330

The only real problem with the third engine was that it tended to be in the tail. On the off chance that it blew up, there was a good chance of it taking out the hydraulics for the flight controls. Not good.

$$$ mostly, in production, maintenance & operation

they would like to go to one, but it wont fly with "0" engines in an emergency

FAA rules used to require > 2 engines for over water flights, incase one failed.
With newer more powerful engines, 2 engine planes are now certified for over water flights.
Even older 737s with newer engines are now used over water too.

Damn if an engine fails it fails. I don't give a ***** if it's over water or land.

Its also pretty noisy back there, from what I remember.

The L-1011 and DC-10 used three engines to achieve a longer ETOPS (Engines Turn Or Passengers Swim) and thus able to cover long distance routes over water without stops with the then-current engine technology.

The B727 was a compromise a/c designed to fill the multiple needs of airlines for short runway capability, high altitude runway capability and ETOPS.

Newer engines have been certified for longer ETOPS so an extra engine is redundant nowadays. Engines are significantly more powerful now as well.

I also believe they do not have the hush kits, or they are less effective for tail mounted engines.
Despite the enormous size of todays engines, the core engine itself hasn't gotten that much bigger (% wise). The increase in size creates bypass air, which is used to increase the engines effiency and decrease it noise.

:confused:

ETOPS -
It's a time and distance thing. Not a water thing.
It's not all about the engines either.
And then there's crew certification...

Odd as this may sound - I have flown Boeing 757s that were ETOPS certified and some that were not. Both with the same RB211 engines.

As for the Q - Post #2 from H-Town pretty much answered the OP question.

You are right - In fact, they've gotten smaller.

Right, time/distance...to a suitable landing site. I maintain that the driving force is over water ops because it just so happens that there are more suitable landing sites on land than in the middle of the Pacific.

FWIW, see attached great circle mapper with 60 and 120 min ETOPS on rte to SYD from LGA via SFO...light blue is 60min...all of the continental US is within 60min B757 ETOPS. Not so for mid-ocean.

That answers why I've seen similar a/c at terminals, some with ETOPS on the nose gear door, some without.

Isn't it also true that tri-jets were tail heavy which caused some interesting handling characteristics? (I remember seeing some photos from a few inexperienced pilots who managed to scrape the tails on landing)

Nope - CG is CG no matter how it's made.

That wasnt because the aircraft was tail heavy.