707 altitudes, and a request

[3spool]

Hi there

Somewhere I've read a claim that , 707's with JT3D engines, had problems flying above FL350. But I have heard of cases of flights at FL390 also.

So,I was wondering, what would be the typical range of cruise altitudes in US in time when 707's were in their prime (60's, 70's )? And how did a typical 707-120B/C or 320B/C behave above say FL350.
Was there a significant disadvantage when compared to modern airliners?
What would be the highest usual altitude that airlines operated in cruise for these planes.
Again, rule out planes with JT3C, I'm asking about JT3D planes.


P.S. Does anyone have any good picture (taken by himself) of a JT3D engine with the nacelle taken off, and is willing to share?

[GK430]

Can't help much, but my old man flew -138B's at Fl 41,0 quite regularly.
I do not recall the 320's operating up there when he flew them.

The VC.10 on the other hand ....higher.

[3spool]

thanks

Well I think 320's do have a lower ceiling. Boeing site says 36000 feet for 320B.
JT3C engined 707's have it at 43000, while 120B has it at 42000.

But that's all theory, the reason I asked this question here among the pilots (and sons of pilots, in your case), is because I wanted to know, just how practical and common was to fly this craft above fl350

[BelArgUSA]

3spool -
xxx
I think you mis-understand "JT3D problems" above FL350, or 390...
The older engines (JT4A) were turbojet engines.
These operated best at high level, FL 370, 390, 410...
xxx
The JT3D were turbofans. They were more efficient at FL 330 or 350.
We rarely operated above FL 370 with the JT3D airplanes.
At higher levels, they did not perform as nice, as the "straight JT4A".
xxx
For info - the JT4A-11 were 17,500 lbs/thrust engines.
The JT3D-1 were 17,000 lbs/thrust, JT3D-3B were 18,000 lbs/thrust.
Most 707-100 and 720 had JT3D-1 engines, JT3D-3B on 707-300B/C.
xxx
The same problem existed with DC-8s...
I flew both 707 and DC8s...
xxx
:ok:
Happy contrails

[BelArgUSA]

Maximum operating level - all types 707 and 720 is 42,000 feet.
xxx
:8
Happy contrails

[3spool]

Well, I was referring to this site:
Boeing: Commercial Airplanes - 707 - 707 Specification (http://www.boeing.com/commercial/707family/product.html)

It says 320B is limited to 36000, is this a mistake? It does seem quite low

[3spool]

Well, yes, I know that turbofans are not as efficient, close to 40 000, but that goes for turbofans in general. In theory, newer high-bypass engines would be even more inefficient, at those levels than older low-bypass engines, right?

Now that I searched the archives, I noticed it was your comment that I read in the first place that made me ask this question, small world I guess.

Anyway. After reading your original post, I got the impression that above 350 JT3D was in some was worse in performance than other, modern airliners.

These days, most airliners can fly above 40,000 without problems, for various reasons, avoiding weather, or due to heavy traffic or whatever.
So are you saying that old planes like 707, did not find this any more difficult than modern jets (economy aside).
Meaning, could you climb to FL420 on a regular passenger flight, without significant risk of stall?

[BelArgUSA]

3spool -
xxx
The most "modern" aircraft I flew last, was the 747-200/300.
With the 747, the highest we climb to, is FL 290 when heavy.
Only at light weight, did we climb to FL 360/370, rarely was any higher.
Although all the 747s are certificated to 45,100 feet.
Sure, we could go higher, if we were lighter. Empty airplanes...
xxx
Airplanes do not go to "high level" immediately. Certain you know this.
As pilots we do not look at "what is the MAX LVL" we can "go to".
We want the level at which we get the highest "nautical air mile per 1000 kg of fuel".
Is like comparing how many km you can drive with a VW Polo with 1 liter/petrol.
xxx
The only one 747 frequently flying higher was the 747-SP.
The 747-SP climbed initially to FL 370, and ended cruise at FL 430/450.
Same wing as the other 747s, but much lighter aircraft weight.
xxx
When you climb in the troposphere = loss of pressure and colder temperature.
Loss of pressure makes a loss of power, but cooler temperature helps.
At the tropopause (11,000 m - 36089 ft), the lapse rate (temp) stops (-56ºC)
So you do not "gain" much climbing higher, if temperature is not cooler.
xxx
:ok:
Happy contrails

[3spool]

Yes, I know, the optimum altitude changes during flight as the aircraft gets lighter. I don't know though how they used to do it in old days before FMC system, but I do know the FMC displays the most efficient altitude for a give weight during flight.

I was just trying to clear up a confusion. I though the JT3D engines had a disadvantage over other turbofan engines.

[BelArgUSA]

3spool -
xxx
The FMC is just a modern PMS - Power Management System.
PMS exists in 747s since the early 1970s... Nothing new, just more modern.
In the old days, we just read performance data from pages of paper manuals.
And nowadays, it is a "page" on a screen.
xxx
The last 747s that I flew were equipped with FMC...
There was no change in the way the aircraft was flown.
The only improvement was navigation. Power management is about same.
Our LTN-92 INS were able to navigate as good as FMC can.
xxx
As far as the most "efficient level", that is the "best NAM/1,000" -
It is some 1,500 to 2,500 ft below the "MAX LVL" of the aircraft at that weight.
And that is for all the planes I flew... 707, 727, 747 and DC8...
Do not need a FMC to find out about that.
xxx
Another interesting fact is the following (about different engines) -
I flew DC8s with 2 different engines. The JT3D and the CFM-56.
Is the DC8 with CFM-56 able to fly higher than the DC8 with JT3D...?
No Sir...!!! At equal weight, equal level is maximum...
Example -
A DC8-63F (JT3D) can cruise at FL 330 maximum if at a weight of 300,000 lbs.
A DC8-73F (CFM-56) cannot cruise any higher. Still FL 330 if at 300,000 lbs weight.
Obviously, the -73F has better range, and burns less fuel...
xxx
:8
Happy contrails

[3spool]

Thanks for all the valuable input

Now, the previous poster mentioned his father, flying 707's at FL410 "quite regularly".
Why would that be? What reasons might a pilot have to fly a 707 that high, other than weather issues, specially considering that there was not as much traffic in those days as there is now?

[BelArgUSA]

The 707-138B was an option of a short body, lighter weight 707-100.
Only one airline decided to order the type - Qantas, about 12 of them.
Fuselage was about the size of 720. Probably configured for 100 passengers.
Obviously being light weight, it would fly often at FL 390 or 410.
xxx
John Travolta's airplane is a 707-138B.
:ok:
Happy contrails

[3spool]

Oh, I didn't know 138 was not the same type as 12x. I assumed the numbering went from 120 up for different airlines, and eventually got to 138.

[Groundloop]

RE the -138, the 38 is the Boeing customer number for QANTAS, hence there later 707s were 707-338Cs, the current 747 are 747-438s, etc.

However QANTAS did request a specially short body for their 707-100s to get the extra range that they required at the time. But as QANTAS were the only airline to buy the special short-body version it is a unique version that is a 707-138 because it was bought by QANTAS, not called a -138 because it had a short body.... Going round in circles now, but hope it makes sense....

[3spool]

Yes, It makes sense, thanks

[GK430]

Father used to fly a pair of the ex-QF -138B's.
Fl 41,0 was great on a Saturday down A34 to LEPA - even in those days it was crowded airspace (no RVSM) and a/c comparatively light.
Also latter stages on transatlantic flts. or empty positioning flts.

When flying the SP as BelArgUSA quotes, Fl 45,0 was easily attainable after
burning off fuel on 10+ hr sectors.

[3spool]

One more thing, what then would be the difference between this 138B and a 720? Isn't 720 a shorter 120?

[diddy1234]

The 720 is narrower I think.

[411A]

The 720 is narrower I think.

No, same fuselage cross section.
However, there is one other difference between a 720 and a -138B...the latter is just a tad shorter in length.

[BelArgUSA]

Hola 3spool -
xxx
My way to recognize the 707/720 were the overwing exits.
One per side on the 720, and two for the 707, therefore, the 138B had two.
Exception - Eastern Airlines had 720-025 with 2 overwing exits per side.
xxx
Some spotters imagined that the HF antenna was missing on 720s.
Not true, many flew outside of the USA, and had the HF antenna installed.
Some 707 used US domestic flights only (TWA) had no HF antenna.
xxx
Mentioning 707-720 differences, we could spend weeks.
And if I mentioned a difference, there would be another "exception"...
How many 707-720 build... some 800...? - 799 of them were... different.
xxx
One thing I never did with Boeing, regardless of model, is generalize.
With PanAm, our 707 manuals had 400 pages, of which 350 pages of differences...!
PanAm had 747-121, 221F, 123, 238, 212, SP21, SP27, which ones do I forget...?
If a Ppruner says "a 734" - I would answer "which 737-400 is it...?"
We pilots have a saying when entering a Boeing... "where are the switches on this one...?"
xxx
:D
Happy contrails

[GotTheTshirt]

3 Spool,

During the Israeli raid on Entebbe the Command center to mission communications were handled by an IAF B707 with JT3 engines.
The aircraft was well above 45,000 for some of the relays.:cool:

Does anyone remember the project to take the world freefall parachute height record for the US? I think the Russians held the record at that time.

It was using an ex MEA B720.
The aircraft was to be stripped out and the para guys ( 12 I think?) were to go out via a steel tube from the cabin through the wheel bay?

[3spool]

That was with JT3C engines I assume?

[BelArgUSA]

The JT3C-6 (707-100) stopped being operated about 1975...
The JT3C-7 (720) basically a couple of years later. Maybe 1980 at worst.
So if any JT3, these were JT3D fans.
That applies to most if not all 707-100/300 or 720 used in the 1980s.
xxx
:8
Happy contrails

[3spool]

I think this event happened in 1976 , that's why I asked if it was JT3C...well that and the altitude, I'm not sure how JT3D could reach it at all

[rubik101]

I flew the 720 in the 80s with Monarch with JT-3s and we generally blasted straight to FL 370 or 390 and on the Canaries flights would go to FL 410. We burned tons of fuel but in those heady days no-one gave a shyte.
Certified max alt was 410 due to pressurisation controller from the 707.
We also had a 320C for a time on the St. Lucia flights and that would criuse at 410 for the latter half of the trip.
Ah, happy days of seven day layovers in the sunshine in Castries or Hurricane Hole!!!!
Performance was all derived from a book full of charts and graphs, helped by a PDCS. Seemed to work in those days.
FMC is just an electronic book after all is said and done.