Blackbird
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B-707/DC-8 Self-Start Systems

Mon Jun 25, 2007 5:25 am

What kind of means did the Boeing 707, Douglas DC-8's, the Boeing 720, and other such aircraft of those era use to start their own engines while on the ground? How did they work?

None of these aircraft had an APU system...

Andrea Kent
 
charlienorth
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RE: B-707/DC-8 Self-Start Systems

Mon Jun 25, 2007 5:35 am

All airstarts,the 707/720 normally started 3,4,2,1 if I remember correctly,the DC8 generally was the same but often times we would just start #3 and disconnect air and electric and perform cross bleed starts on the remaining engines,they did not like to do this on the 707's,the 70 series 8's did have an APU but it had problems and many times couldn't supply both air and electric during a start..on a side the Caravelle had an electric starter.
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Blackbird
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RE: B-707/DC-8 Self-Start Systems

Mon Jun 25, 2007 6:52 am

How does an airstart-system work?

Andrea K
 
lowrider
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RE: B-707/DC-8 Self-Start Systems

Mon Jun 25, 2007 7:06 am

Quoting Blackbird (Reply 2):
How does an airstart-system work?

Typically air is supplied from a high pressure source, either a compressor or a pressurized bottle, through a fitting on the outside of the aircraft to a common manifold. The air is then routed to the desired starter. Once running, bleed air from the engines can pressurize the duct and be used for a "crossbleed" start.

The idea is not new, however. Radial engined aircraft have used air start systems for decades. They were commonly found in colder climates. Air is used to start the engine rotating, then fuel and spark are introduced. Air was supplied from a small bottle mounted on the aircraft that could be recharged with a hand pump, if needed. Some radials used blank shotgun shells to generate a pulse of compressed air.
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Blackbird
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RE: B-707/DC-8 Self-Start Systems

Mon Jun 25, 2007 9:00 am

The airstart systems were external? I thought they were part of the plane

Andrea Kent
 
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Jetlagged
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RE: B-707/DC-8 Self-Start Systems

Mon Jun 25, 2007 9:22 am

The starter motor, starter valve and ducting is part of the plane. Without an APU an external air source must be provided to start the first engine. Crossbleed can then be used to start the rest.
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charlienorth
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RE: B-707/DC-8 Self-Start Systems

Mon Jun 25, 2007 9:22 am

No the airstart unit as a large piece of ground equipment that as Lowrider posted supplies high pressure air to the starter on the engine,resulting with rotation of the engine,with fuel and spark gives us our start,there is receptacle on the aircraft to hook it up to,you than select the air to the aircraft..normal procedure would be to address the captain through the headset..."Ready for start'...."Ready to start #3"..."you are clear start #3".....after 3 is started.."ready on #4"...'you are clear four" this is using a 707,we would go through 2&1 with the same discussion after the final engine was started the captain would say"we've had four good starts..you are clear to remove air and electric" after this was accomplished and all was disconnected and panels closed we would do the pushback procedure,This is also what we still do when the a.p.u is inoperative..the a.p.u is great..the amount of ground service equipment needed for an aircraft without an a.p.u. is a pain in the neck...besides the air start unit and groung power you also need an air conditioning or heat unit.
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lowrider
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RE: B-707/DC-8 Self-Start Systems

Mon Jun 25, 2007 9:23 am

Quoting Blackbird (Reply 4):
The airstart systems were external? I thought they were part of the plane

The aircraft you refered to used external air starting. You can have an internal system, but it requires an on-board source of compressed air, typically an APU.

In the broader sense, airstart simply refers to using compressed air to start the engine moving before introducing fuel and ignition. On a jet engine, compressed air is usually released or "bled" into either the engine itself, or across a starter turbine connected to the compressor. Once a minimum RPM is reached, the airflow through the engine is sufficient to sustain combustion and fuel and ignition are introduced.
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Blackbird
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RE: B-707/DC-8 Self-Start Systems

Mon Jun 25, 2007 10:10 am

I remember the 707-138B had an interesting start system. You pressed a button, then started moving the fuel-levers forward to the idle position... the engine noise got louder and such, and eventually lit-off and idled out...

What kind of system is this?

Andrea Kent
 
fr8mech
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RE: B-707/DC-8 Self-Start Systems

Mon Jun 25, 2007 10:20 am

Quoting Charlienorth (Reply 6):
supplies high pressure air to the starter on the engine

An airstart actually supplies low pressure air (in the 35 - 40 pound range) at high volume.

As I recall, some B707 type aircraft did have a single shot start system installed. It was comprised of a set of nitrogen bottles and the associated controls, tubes and valves. As implied by the name, you had one opportunity to start an engine, after which you used cross-bleed air to start the other engines. The bottles were charged on the ground from a high pressure source.

I do know that some DC8's had an APU installed in the #2 pit area.

I believe some military aircraft use a cartridge start system. I don't know much about it, but I suspect it uses an explosive charge to generate the necessary pressure and volume.
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charlienorth
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RE: B-707/DC-8 Self-Start Systems

Mon Jun 25, 2007 10:30 am

Quoting Fr8mech (Reply 9):
An airstart actually supplies low pressure air (in the 35 - 40 pound range) at high volume

my bad, I meant hi volume,some aircraft need two start units,the Y-adapter can be a mother to handle after a start.

Quoting Fr8mech (Reply 9):
I do know that some DC8's had an APU installed in the #2 pit area.

Mostly on the 70 series,I understand thay had a tendency to overheat..TransAmerica had that set-up...I don't know if UPS improved it when they got those AC

the ex military pilots at UAL always ask about a "bottle start"
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fr8mech
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RE: B-707/DC-8 Self-Start Systems

Mon Jun 25, 2007 10:48 am

Quoting Charlienorth (Reply 10):
I don't know if UPS improved it when they got those AC

I believe they were removed before entering service with UPS. I want to say it was 2 aircraft. 819 and 812, maybe? I'd have to look at the aircraft.
When seconds count...the police are minutes away.
 
VC-10
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RE: B-707/DC-8 Self-Start Systems

Mon Jun 25, 2007 11:00 am

The 707's I worked on had large HP air bottles located in the wing to body fairings aff of the wing for engine starts where there were no air start trucks on station.

The VC10 had a combutor start system where air supplied from 3 air bottles located in the tailcone below the rudder was ducted to a small combustor attached to the #3/4 eng firewall. In the conbustor kerosene was mixed with the air and ignited. The exaust gasses were then supplied to the #3 Eng starter to turn it & fire up #3 engine. Once again this was a last ditch arrangement for when there wasn't an air start truck was available
 
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jetmech
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RE: B-707/DC-8 Self-Start Systems

Mon Jun 25, 2007 11:28 am

Quoting Blackbird (Thread starter):

Ah yes, the use of the start cart! Many times we have had to use a diesel driven start cart to start the engines of 747's or A330's. The massive cloud of thick black smoke that comes out of the roof mounted exhausts of the diesel as it starts to spool up the engine is amazing  Smile  bigthumbsup  ! With respect to the 707, I believe that the ones I worked on a while back had an APU fitted as a modification. Nonetheless, to spin the engines in the hangar, we used to use a start cart that was basically a 737 APU on wheels. The sound of this thing spooling up was frightening!

I seem to remember from a book I flicked through that the SR-71 uses a piston engine for starting as well. In this case, I think that the start cart is a supercharged V-8 engine. This engine is connected to what I assume would be the external gearbox on the J-58 by a vertically orientated shaft. This shaft then mechanically turns the engine over for starting.

The air-conditioning and start cart trucks are usually very large rigid chassis vehicles. This is in contrast to the APU which is about the size of a large refrigerator. It has always fascinated me how you need several large diesel engine powered devices (air-con, electrical) to replace one broken down APU.

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411A
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RE: B-707/DC-8 Self-Start Systems

Mon Jun 25, 2007 11:55 am

Some ( but certainly not all) B707 aircraft had a high pressure start system, which consisted on one (PanAmerican had two, however) high pressure air bottle installed in the left wheel well (PanAmerican, L&R side) which provided high pressure air to the stater, to provide engine rotation.
In cases where external electric power was not available, a BATTERY start was completed.

The start SWITCH (either rotary or toggle, depending on the mod status...and NOT a 'button') was moved to the 'high pressure start' position for these HP starts and, the fuel lever was moved to the 'start' position at the first sign of N2 rotation.
When the engine was running in a stabilized condition, the start lever was moved to 'run', the GFR, GB, and BTB were closed on this engine, and full electrical power was then available.
The ONLY engines that could be started with the HP system were engines 2 & 3.
Each of these engines had turbocompressors installed, and the TC was started at this time, the power advanced on the operating engine, and a cross-bleed start procedure was then used to start the remaining engines.

Usually, number one engine was equipped with a TC, but the HP (bottle) air could not be routed to this engine, for starting, so it was 2 or 3 only.
 
VC-10
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RE: B-707/DC-8 Self-Start Systems

Mon Jun 25, 2007 5:34 pm

Quoting 411A (Reply 14):
Usually, number one engine was equipped with a TC,

Do you mean number "one engine was NOT equipped with a TC"?
 
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RE: B-707/DC-8 Self-Start Systems

Mon Jun 25, 2007 8:28 pm

Quoting VC-10 (Reply 12):

The VC10 had a combutor start system where air supplied from 3 air bottles located in the tailcone below the rudder was ducted to a small combustor attached to the #3/4 eng firewall. In the conbustor kerosene was mixed with the air and ignited. The exaust gasses were then supplied to the #3 Eng starter to turn it & fire up #3 engine. Once again this was a last ditch arrangement for when there wasn't an air start truck was available

That might have been the case with military VC-10, but none of BOAC aircraft had this facility. I understand that the pre production aircraft had a HP bottle in the tail cone ,but I thought the only civilian operator to retain this was Ghana Airways , but I could be wrong

The emergency starting system for BOAC was to get a group of HP bottles [6 I think] connected in parallel and you used them to start one engine then cross bleed start start the others. There was a special procedure for this though and if it was not followed there was a chance you would blow some of the aircraft ducting with too high a pressure air.

The Concorde had no APU and no across the ship cross bleed either ,only x-feed between the adjacent engines on either side. It was normal therefore to have two Ground air start units one per side and start the 2 inboard engines and the x-bleed start the outers after push back from their adjacent engine.


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411A
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RE: B-707/DC-8 Self-Start Systems

Tue Jun 26, 2007 1:28 am

Yes, some operators eliminated the turbocompressor from the number one engine (altho the cowling stayed much the same)...American Airlines comes to mind, with some models of their B707's.
 
411A
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RE: B-707/DC-8 Self-Start Systems

Tue Jun 26, 2007 2:44 am

Whooops, my mistake.

Scratch engine one, replace with engine FOUR.

So, HP start air available only to engines two and three. T/C's on those engines, and (usually) number 4.
American, on some models, eliminated the T/C from engine 4.

There, that looks better.
 
DeltaGuy
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RE: B-707/DC-8 Self-Start Systems

Tue Jun 26, 2007 2:46 am

Quoting Lowrider (Reply 3):
Radial engined aircraft have used air start systems for decades. They were commonly found in colder climates

The Yak-52 and CJ-6 are two that come to mind...designed to be operated in Siberia-style conditions, cold and rigid engines. You only get a few shots at starting it before the air tank is gone, hence why alot of folks bring along a scuba tank for those missed starts.

DeltaGuy
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USCGC130
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RE: B-707/DC-8 Self-Start Systems

Tue Jun 26, 2007 6:01 am

Quoting 411A (Reply 14):
Each of these engines had turbocompressors installed, and the TC was started at this time, the power advanced on the operating engine, and a cross-bleed start procedure was then used to start the remaining engines.

Interesting. I knew that the TCs supplied air for cabin pressurization, but until now I thought that the air used for cross-bleed engine starts was tapped directly from the engine compressor, C-130 style.

I didn't realize that the turbocompressors needed to be manually started. It had always been my impression that they were connected directly to the engine via a radial shaft or an accessory drive, and spun up automatically when the engine did.

What is the engines' percent RPM at idle? The relevance is that reading about cross-bleed starts on the KC-135 and now the 707, I note that power needs to be advanced on the operating engine before the remaining engines are started. This struck me because no power advance is necessary on the C-130 -- but of course the T56 is a constant-speed engine and runs at 100% RPM at normal ground idle. I'm curious just how much the power needs to be advanced on a JT3/4 in order to generate sufficient manifold pressure.
 
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RE: B-707/DC-8 Self-Start Systems

Tue Jun 26, 2007 6:29 am

Quoting 411A (Reply 17):
Yes, some operators eliminated the turbocompressor from the number one engine (altho the cowling stayed much the same)...American Airlines comes to mind, with some models of their B707's.

Assume you're referring to the early non-turbofan 707s where the engine cowlings/pylons looked the same on all engines. But on JT3D turbofan-powered 707s it was easy to tell that the No. 1 engine lacked the turbocompressor as it had a much thinner pylon than the other 3 engines.

Almost all 720s only had 2 turbocompressors on #2 and #3 engines, again easy to spot by the thinner pylons on #1 and #4 engines on JT3D-powered 720Bs.
 
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RE: B-707/DC-8 Self-Start Systems

Tue Jun 26, 2007 8:52 am

Quoting Uscgc130 (Reply 20):
It had always been my impression that they were connected directly to the engine via a radial shaft or an accessory drive, and spun up automatically when the engine did.

IIRC, the TC's on the 707 were driven by bleed air taken off the engine. I was sure that this bleed was taken off after the combustion chamber, but I recall someone stating in an earlier thread that is was in fact taken off before the combustion section.

Quoting Viscount724 (Reply 21):
But on JT3D turbofan-powered 707s it was easy to tell that the No. 1 engine lacked the turbocompressor as it had a much thinner pylon than the other 3 engines.

Did Conway powered 707's have TC's on all four engines ?


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411A
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RE: B-707/DC-8 Self-Start Systems

Tue Jun 26, 2007 10:33 am

9th stage bleed air was the source of air to operate the turbo compressor.
T/C's needed to be started AFTER engine start, via an electrical toggle switch on the F/E's panel and were then operated to either supply pressurization and air conditioning, or for cross bleed starting of the remaining engines.
If, for example, the number three engine was started first, it's T/C was then started, the throttle was advanced to 70% N2, air conditioning packs selected OFF, and a second engine (usually number 4) was then started, it's T/C' started, and the number three engine was returned to idle thrust, as the output from two operating T/C's with corresponding engines at idle was sufficient to start the remaining two engines, normally number two first, then number one.

Regarding RR Conway powered airplanes, normally 4 T/C's were fitted, but some operators removed the T/C from the number one engine, but the cowling appearance remained the same.

Going further, could the cabin of the B707 be pressurized with straight bleed air, not T/C air?
The answer is yes, but only on certain B707's, and then only on the airplanes that were equipped with air cycle machine (ACM) air conditioning packs.
NOT possible with those airplanes that had vapor cycle air conditioning, either old or new style.

Many MANY different variations, according to original customer requirements.

PanAmerican, for example, had quite a mix...vapor cycle (new), vapor cycle (old), and ACM air conditioning were fitted to models in their quite large fleet.
 
Viscount724
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RE: B-707/DC-8 Self-Start Systems

Tue Jun 26, 2007 11:15 am

Quoting Viscount724 (Reply 21):
Assume you're referring to the early non-turbofan 707s where the engine cowlings/pylons looked the same on all engines. But on JT3D turbofan-powered 707s it was easy to tell that the No. 1 engine lacked the turbocompressor as it had a much thinner pylon than the other 3 engines.

Re my comment above, have discovered after some further research that AA was unusual in ordering 707-320B/Cs with only 2 turbocompressors. AA's -120Bs, both those converted from turbojet -120s, and those delivered new as -120Bs, also only have 2 turbocompressors. I believe those may be the only 707s built with only 2 turbocompressors. Photos below showing the narrow pylon on #4, same as #1, like the 720B.

-120B

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-320B and -320C (can see all 4 pylons in the 2nd photo)

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Photo © A. C. LEVESQUE



Quoting 411A (Reply 23):
PanAmerican, for example, had quite a mix...vapor cycle (new), vapor cycle (old), and ACM air conditioning were fitted to models in their quite large fleet.

I noted a comment in an earlier thread (there are quite a few on this subject) mentioning that PA also removed the turbocompressor from engine #4 on some 707-320B/Cs but didn't change the pylon so you can't tell whether there is one or not.
 
CaptOveur
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RE: B-707/DC-8 Self-Start Systems

Tue Jun 26, 2007 11:33 am

Quoting JetMech (Reply 13):
I seem to remember from a book I flicked through that the SR-71 uses a piston engine for starting as well. In this case, I think that the start cart is a supercharged V-8 engine. This engine is connected to what I assume would be the external gearbox on the J-58 by a vertically orientated shaft. This shaft then mechanically turns the engine over for starting.

Two buick racing V8s.. I think they were somewhere in the 400cu inch range.
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Dougloid
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RE: B-707/DC-8 Self-Start Systems

Tue Jun 26, 2007 10:29 pm

Quoting CaptOveur (Reply 25):
Quoting JetMech (Reply 13):
I seem to remember from a book I flicked through that the SR-71 uses a piston engine for starting as well. In this case, I think that the start cart is a supercharged V-8 engine. This engine is connected to what I assume would be the external gearbox on the J-58 by a vertically orientated shaft. This shaft then mechanically turns the engine over for starting.

Two buick racing V8s.. I think they were somewhere in the 400cu inch range.

A lot of our older Hobarts at Garrett had Chrysler Hemis.

We had two air sources at Douglas for pressurizing MD11s on the ramp and the two together would just about git r done. One was a Ford truck with a Roots blower and two Detroit Diesel 8V71s mounted back to back.

The other was a blower cart with a single Detroit Diesel 12V71 with twin turbos hooked to a monster Roots blower. A thing of beauty.
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clipperno1
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RE: B-707/DC-8 Self-Start Systems

Tue Jun 26, 2007 11:51 pm

And what do you do when you land your DC8 at a place where all GPU's are inop?
Yeah, to the joy of everybody at the airport and around, you leave one engine running. This will expedite the handling and cargo break process at even the most rural airport in the world.  razz 
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charlienorth
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RE: B-707/DC-8 Self-Start Systems

Wed Jun 27, 2007 1:31 am

Quoting ClipperNo1 (Reply 27):
And what do you do when you land your DC8 at a place where all GPU's are inop?
Yeah, to the joy of everybody at the airport and around, you leave one engine running. This will expedite the handling and cargo break process at even the most rural airport in the world.

I remember the big deal in 1983 when Global International landed a 707 in LSE,no airstart available,they had to keep an engine running and Republic's ground crew  old  were refusing to work it because of it,if it was force or bribery I don't know because they finally worked it and got it out of town.
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broke
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RE: B-707/DC-8 Self-Start Systems

Thu Jun 28, 2007 4:41 am

Douglas had an option on the DC-8 which included a compressed air reservoir mounted in the mid service center which was located between the forward lower cargo compartment and the main landing gear wheel well.
I've seen the installation on some ex-Swiss Air and ex-UTA DC-8's among others. By the time I saw it, the system was not operational and was being removed during a cargo conversion.
It was intended to be used at remote airports with few facilities and was used only to get one engine started on the ground. Once one engine was running there was electrical power and cross-bleed air to start the remaining engines.
I am not sure if the reservoir could be recharged to a sufficient pressure using engine bleed air or not.
 
Tristarsteve
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RE: B-707/DC-8 Self-Start Systems

Thu Jun 28, 2007 7:04 am

Quoting Uscgc130 (Reply 20):
What is the engines' percent RPM at idle? The relevance is that reading about cross-bleed starts on the KC-135 and now the 707, I note that power needs to be advanced on the operating engine before the remaining engines are started.

Older engines with low bypass ratio did not produce enough air at idle for a x bleed start.
The B737-200, which idled at 60pcN2 needed to be run up to around 80pc for a Xbleed start. This made a lot of noise so it was normal to start both engines at the gate off the air starter.
Modern engines produce enough, or nearly enouigh, air at idle for Xbleed start.

Quoting VC10 (Reply 16):
The emergency starting system for BOAC was to get a group of HP bottles [6 I think] connected in parallel and you used them to start one engine then cross bleed start start the others.

When Braathens was its own airline, their air starter at Stavanger was a big air bottle. The size of a small bus that was pressurised to 40psi by a compressor. Worked fine at starting B734s, but you only got one go. Then you had to wait 2 hours for it to recharge.
At ARN T2 there is a larger bottle installed under the ramp. A hose comes out of the ground at each gate, and visitors are amazed to see a single hose starting an RB211 in silence. Until the engine starts there is no noise at all! Brilliant idea when you usually have to stand beside a big diesel air starter anywhere else.

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