View Full Version : L-1011 cabin altitude

19th Apr 2008, 23:12

I understand that L-1011 cabin altitude can be maintained at Sea Level until 22.000'.

But I have a little doubt... If we are climbling to e.g. 35.000ft, will the cabin start climbing only when passing 22.000' or will it start climbing since take-off?

In the first diagram it seems the cabin starts climbing from the moment we take-off:



20th Apr 2008, 00:35
Depends what cabin altitude is selected does it not?

Old Fella
20th Apr 2008, 00:58
Normal practice in my experience has been to set planned cruise altitude plus 1000' on the pressurisation controller. This gives a buffer between the pressure differential you will hold and the max differential allowed. The rate of change in cabin altitude is normally set to give approximately 500'/min rate of change in the climb and, for pax comfort, a maximum of 300'/min on descent. If you are cruising at the lower level where the cabin will be maintained at sea level the rate of pressurisation will be such that the cabin remains at sea level (assuming your airfield of departure was at sea level). If you are climbing to the higher levels the rate of pressurisation will be such that the cabin altitude will climb steadily from whatever it was at your departure airfield to whatever it will be at your cruise level. On all the aircraft I crewed the cabin pressure controller rate could be changed if required, however most had a "normal" index at which the rate was set. Have not been in a L1011 since 1986, so the actual figures escape me.

20th Apr 2008, 01:01
Most aircraft can hold sea level cabin altitude to 22,000 ft. After take off they are normally set for planned cruise altitude. If you go high the cabin usually ends up around 8,000 ft. It starts it's climb right after take off.

20th Apr 2008, 03:24
Most aircraft can hold sea level cabin altitude to 22,000 ft. After take off they are normally set for planned cruise altitude. If you go high the cabin usually ends up around 8,000 ft. It starts it's climb right after take off.

L1011 the same.

20th Apr 2008, 03:53
If you have the auto controller set at sea level then you would maintain a cabin at or near sea level until 22,000 feet aircraft altitude, probably near max differential pressure also
If the aircraft climbs say to 31,000 feet with the auto controller still set at sea level then the cabin would climb and try to maintain a max differential pressure.
If the max diff pressure is exceeded then the relief valves would open.
Red faced item! LOL
Dont remember the actual numbers since going back to the 747.

Normally the cruise level is set prior to takeoff on the scale and cabin climbs to the preset level at whatever rate you have selected.

Same situation on decent, if you were to forget and leave the cabin altitude at the cruise flight level then the controller would maintain this until max diff pressure was met and then start descending the cabin.

Little hard on the ears as the rate of decent for the cabin would match the aircraft depending on the situation.

20th Apr 2008, 07:54

I'm asking about the L-1011 because it's my work place and I am redoing the cabin crew manual and I'm trying to understand how pressurazation works. I've not been flying in the last days so I cannot ask and see that in loco.

I really appreciate your help and I have another question:

I don't know the corresponding numbers in the ALT SET tape between FLT ATL and CAB ALT. I see that one way of getting sea level until 22.000' is by leaving the FLT ALT at sea level in the ALT SET. But if prior to take-off we do select FLT ALT of 22.000' (or anything below that and above sea level) in the ALT SET, what do we get in terms of CAB ALT? Still sea level or something higher?

Old Fella
20th Apr 2008, 11:28
CS-TMX, Pressurisation of the aircraft pressure hull allows an artificial cabin altitude to be maintained when in flight. Simply, all that beaut conditioned air which is directed into the aircraft is allowed to discharge at a predetermined rate. Because there is a limit to the pressure to which the aircraft can be pressurised, let's say 9.4 psi or thereabouts, the aircraft (such as the L1011) is able to maintain a sea level cabin altitude up to around FL220. This means that at FL220 the cabin will be pressurised to around 9.4psi differential. That is, 9.4psi higher pressure than the ambient temperature in which the aircraft is operating. If the FltAlt was left set at FL220 the cabin would begin to climb as the aircraft climbed above that level because it will only maintain that same pressure differential. If it tries to "over pressurise", the cabin controller should not allow it to do so, but in the event that it does the "safety Valve" would open to relieve the pressure and so prevent airframe damage. It is too many years since I was operating on the L1011 to be specific, but lets say that the FltAlt side of the scale says 22000 and opposite is says ) for the CabinAlt, if you were to set 22000 before take off, the cabin would maintain your departure field elevation initially. If that were sea level, you would maintain that up to FL220. If your departure airfield was, say, 2500' AMSL, then as you climbed toward FL220 the cabin altitude would slowly descend to sea level. It is important that as descent is started the cabin controller is set to the destination airfield elevation to arrive on ground at that airfield with zero cabin differential pressure.
As far as the rate of change of cabin altitude is concerned, this "rate" is set on the same controller on which you select your FltAlt. I am impressed that as a Flight Attendant you are keen enough to want to know more about the control of the environment in which you work. My advice would be to speak with your friendly F/E next time you go flying and get him/her to show you first hand how it is done.

20th Apr 2008, 23:13
Thanks again for your help!

I am impressed that as a Flight Attendant you are keen enough to want to know more about the control of the environment in which you work. My advice would be to speak with your friendly F/E next time you go flying and get him/her to show you first hand how it is done.

As I said, I am redoing our cabin crew manual and I wanted to know a little more about it. And I'm also an aerospace engineering student! Working as a F/A was the only way to have the chance to fly the L-1011 again! And I love my job! Great plane and beautiful girls :O

21st Apr 2008, 00:51
Great plane and beautiful girls

The girls are only a side benefit.
Anyone who has flown the Lockheed L1011 has truly experienced the very finest that long ago engineering expertise could truly accomplish...bar none.

Old Fella
21st Apr 2008, 02:34
My sentiments exactly 411A. Still the only one I know about with DLC and one of the best Autoland systems around. If it had not been for the delays in developing the RB211 Lockheed would have sold many more L-1011 airframes.

21st Apr 2008, 10:07
It was shortsightedness by Lockheed to preclude engine choices for their L1011 customers. Its TriStar was limited to the Rollers.

And the early -22s experienced frequent disc failures, not to mention the engine delivery upheaval due to RR bankruptcy. [This also had caused late delivery of RR powered 747s]

. . . Unlike McDonnell-Douglas, which had offered its tri-motor customers with engine choices. :ooh:

Old Fella
21st Apr 2008, 10:59
What GlueBall says is correct. Lockheed likely should have offered alternatives to the RB211-22, however once the bugs were ironed out the triple spool RB211 family have proved to be extremely reliable and fuel efficient. I know of more than one which remained "onwing" for more than 20000 hrs. Also, unlike the Douglas three holer, I don't ever recall a Tristar "shedding" an engine.

dynamite dean
8th Nov 2009, 22:26
Rather than creating a a new link:

Our lear (45) when we start up has the cabin climbing at 750ft per min when we put the pack on, then falls down slowly is this a normal situation on the ground? Not a big deal but is this just the system doing its test or something or more curious?

many thanks

Old Fella
9th Nov 2009, 04:26
Don't know anything about the Lear, but a bit more info would help. You said that when you "start up" the cabin is "climbing at 750'/minhen you put the pack on then falls down slowly" and ask "Is this a normal situation on the ground"?

Would need to know more info, like does "start up" mean starting a climb? Can you set, manually, a desired cabin altitude for cruise or is it all auto?

galaxy flyer
9th Nov 2009, 04:39
Old Fella and 411a

It is my understanding that the L-1011 design with the center engine on fuselage centerline with an S-duct required a short engine, hence the three spool RB 211. That precluded either the JT-9D or the GE CF-6, which were installed on the other wide-bodies. True or not?


It is not a coincidence that the longest of the three engines is installed in the rudder on the DC-10. Sorry, 11Fan.

Old Fella
9th Nov 2009, 08:19
I am not sure about the length of the engine being the reason for the RB 211 engine being the only engine offered by Lockheed. I would have thought that, despite some early teething problems and late availability with the -22B, the RR was the best option for commercial and, subsequently operational, reasons. As well, I believe the USA Federal government provided financial support for RR Aeroengine division who were bankrupted by the development of the engine. Don't quote me though, just my thoughts on the issue. 411a may have more info. BTW mate, the centre engine of the DC-10 and MD-11 is not mounted in the rudder, but in the vertical stabiliser (Fin). In typical LOckheed fashion the L-1011 was somewhat "over-engineered", but was probably one of the nicest aircraft cockpit environments in which to work ever offered.

galaxy flyer
9th Nov 2009, 17:39
Old Fella

I stand corrected, the DC-10 center engine is vertical stab mounted, but the public perception is rudder-mounted. I was lazy about it. I only jump seated the L-1011, at EAL, and was most impressed in the cockpit size--nearly C-5! Memory might be fading, but compared to the B727, it seemed immense.


Old Fella
10th Nov 2009, 03:27
Never been in a C5, however I think the L-1011 would be hard to top. The B707 & B747 are like a "dog box" by comparison. Boeing, I guess, believe the money comes from the pax and air freight, so their emphasis is on reliablility and maximising earning potential. The Boeings, to me, were not too clever but got the job done without any fuss.

10th Nov 2009, 05:07
....L-1011 was somewhat "over-engineered",
Without a doubt.
Having said this...there is not today a widebody civil jet transport airplane with more redundant systems, than the ...L1011.
A superb example of overengineering?
Absolutely...and nice to fly, as well.:ok:
Now, as far as the original selection of engines are concerned, I must leave this to others to debate, however....we do have one expert here whom I expect will chime in with the correct info....IE: a Lockheed guy for many years.

Brian Abraham
10th Nov 2009, 15:13
Alternative engine from L-1011 Tristar History (http://www.globalsecurity.org/military/systems/aircraft/l-1011-history.htm)

There simply was no easy alternative to the Rolls engines. To turn to Pratt & Whitney for its JT-9D turbofan or to General Electric for its own commercial engine, the CF-6, would cost a year in time and $100 million in development costs. That was because neither of these engines would slip in neatly as a replacement. There would be need for extensive redesign of engine housings and installations, starting with wind-tunnel tests, proceeding through reconsideration of weight distributions

12th Nov 2009, 15:05
There were many reasons that alternative engines were never offered on the L-1011. However, came down to the fact that Lockheed did not have the money required for-designing, re-tooling and re-certifing an alternative engine. Remember after the Lockheed (Dan Houghton) got Rolls Royce out of bankrupicy, Lockheed had to borrow $250M from the US government, just to keep the L-1011 program alive.