B757 air start query
 

The way I read it an airstart is to be done ideally with 2 air start units (although one is sufficeint) to start one engine then following pushback the other engine started using the crossbleed start procedure. The supplementary procedures simply say accomplish start using normal start procedure but I could swear I had read that you had to start eng 1 (left) first then eng 2 with the crossbleed.

On the 733 you had to start 1 first as the ASU connector was very close to the number 2 and so would be a trifle dangerous to start with the ASU man stood there. THere seems to be no such problem with the 757 or indeed any kind of schematic in any of the 'new and improved' (or rather thin) Boeing tech manuals regarding the actual position of the ASU connection points on the aircraft belly. Any such diagram would be greatfully received!

I can't seem to find the reference to this so it may be just remnants of my previous Boeing type. Can someone enlighten me as to what the normal procedure is and where I might find a slightly more comprehensive description beyond the supplementary procedures.

Thanks in advance

Boxjockey

Hello BXJ,

Sorry, no diagram handy, but I can tell you the pnuematic ports are located:

752:
~20M aft of Nose
.6M left of Centerline
.9M right of Centerline

753:
23M aft of Nose
.6M left of Centerline
.6M right of Centerline

This puts the fuselage inlet ports just about abeam the midpoint of the nacelles. 3 Ports for the RB211s - 2L 1R - while the Pratts have 2 ports - one on each side.

Minimum pressure and volume is around 40PSI at 200-250 lbs/min @the connector (or 35PSI cockpit duct press gauge) depending on outlet temp. All of the 37s have the ASU less than 2M from #2 while on the 57s the distance is more like 5M.

I couldn't agree more - the old Boeing materials were indeed more in depth. Of course there were more gauges, fewer all-knowing computers, so I guess a deeper understanding of the machinery was a necessity. :\


cheers !

vapilot

You can start both or either one on a 737 off the air cart. Depends on the mechanics.
Have done 1 air start on a 757 and we only used 1 cart. Don't remember which engine we started first. Wanted 2 carts but only one available. (RB 211 757.)

I understand there are different 'sizes' of air carts, 1 large one will start a 75 or 2 small ones.

The memory is a little rusty on the exact positions, but the basics are that on the 757, the air start is usually positioned behind the wing, so it's not such an issue as to No 1 or No 2 started first, but then the air start has to be removed before the other one is started. If there's an airbridge involved, then it's better to have the airstart on the No 2 side, for ease of access of all the other items, especially if it's a towed unit rather than one built on the back of a small truck chassis.

Ideally, push back is then done with one running, if for no other reason than a 757 with both running is not the easiest of machines to push, unless you've got a tug that normally deals with 747's! If it's a "small" aircraft tug, then both running on a 757 makes things "interesting"!

On the 737, it's a different story, due to the much lower height of the access port for the air. In this case, the airstart pipes are ahead of the wing, and that means that there's no way the operative can go past a live engine on the 737, so it's always No 1, then disconnect.

Single or dual airstart depends entirely on the capacity and condition of the air start unit, and a weak single air start on a 757 can lead to some very anxious moments in the tower when it eventually starts, as it's likely to be VERY smokey, and there's a much higher liklihood of a hot start, as the rotational speed of the engine will be marginal in comparison to the normal speed at which fuel is introduced. On one occasion, I got seconded to another handling company to do an airstart on a 757, and our airstart was not in the best of condition, so it took a LONG time for the core to spool up, and I suspect that the flight deck opened the fuel flow at slightly less than the normal rotation speed as it wasn't going to get any faster, so we were "treated" to a large cloud of very white smoke, and a very quick inquiry from the flight deck to the headset man " is everything OK, as ATC are worried we have a fire". There wasn't a fire, so they recalled the fire service who had already been dispatched, but there were some "interesting" discussions later about that start.

Almost as good as the time when they scrambled the fire trucks because of the clouds of very black smoke that the de icer was emitting:E

Not sure about the 757 but IIRC the start sequence on the 767 was #2 first from a ground air source. The air connection is on the lefthand side and besides the obvious safety benefits it also allows you to use the isolation valve to cut off air to the starter should the start switch fail to release from the GND position. (Just in case your guy on the ground unit is to slow to react) If you started #1 first the only valve in the line is the start valve itself, your only protection should it fail is a quick response from the air cart operator.

The 737 should work the same with the positions reversed. i.e Ground connect on RHS, isolation valve to kill air on #1 engine if required.

On the B757 with RR engines, you need two hoses to start the engines properly. We have a big airstarter with two hoses and that is just fine. Using a single hose airstart unit you are asking for a hot start.
However, in ARN T2 there is a built in airstart system in the gates. It consists of a enormous tank underground pressurised to 40psi. A SINGLE hose comes out the ground, and can start a B757, and a B767 quite adequately. There is enormous mass flow down the one hose. Apart from this I have never started a RB211 on a single hose.

Positioning of the starter really depends on the gate and jetty arrangement. We try and park the airstarter in front of the wing and away from the jetty (very noisy). It is usually quite difficult to achieve easily on any Boeing or Airbus. The DC8 and DC9 are much easier as the connections are not hidden away under the centre fuselage.