What Is A Bleed Kit

[Maricel Fergason]

Inthe f-18 the engines use bleed air from the apu to start. The fire test you perform closes off the bleed air valves in the aircraft. In order to provide bleed air for startup back to the engines you have to cycle them open again. That is the reason you have to move the knob around again.

It won't prevent or hamper your second engine start, as APU air does not pass through a bleed air valve (it will however prevent a crossbleed start, obviously). But with bleed air valves closed, you will have no air conditionning or pressurisation.

Bleed air is air taken from the compressor stage of the engines and used for the ECS (Environment Control System). When you do the Fire test, the valves close and air is no longer taken from the engines. The idea is to get your ECS back up and running as soon as you can, which is as soon as you have AC power on the aircraft, therefore, after the first engine start.

Note that in-flight, you can supplement avionics cooling with ram air via the AV COOL switch EMERG position. It opens a scoop that allows ram air to cool part of the avionics. However, once opened, it can only be closed manually on the ground. I have no idea if this is modeled in DCS as of now.

Bleed air is used for many different things including pressurisation of the cabin, fuel tanks, external fuel transfer, canopy sealing, G-suit pressurisation, gun gas purging, canopy anti-ice and some others I can't quite think of. It's cooled before being used for these things, of course!

The bleed is an extra area that you add to your design to make sure there's no "white border" once the card or flyer is cut. The cutters that print shop use is not 100% perfect, pages might not be aligned or printed perfectly; when you add bleed, you make sure there's color everywhere no matter what.

That goes for business cards, postcards, flyers, covers, banners, etc. Even giant size banner need it unless you don't mind having a banner that is a bit smaller; it will be trimmed smaller if there's no bleed added to your layout!

The only time you don't need to use bleed is when there is absolutely nothing printed on all sides (eg. a design with a white border.) Some small ads in magazine or newspapers don't require it but it's better to provide a file with some bleed if you're not certain.

Another situation where you might not need to add bleed on all sides is when your file is provided as a "printer spread"; for example, a book cover design with the spine, front and back cover on the same layout OR a brochure with a fold OR a greeting card. The bleed will only be necessary for the printer on the outside edges. It's still a good idea to create your own designs (front cover and back cover) with bleed on all sides; it will be easier for you to merge them together later when you'll prepare the final print-ready file.

For magazine, they usually provide a template or precise instructions for bleed but the file still need to have bleed on all sides. The part where the fold or binding is will still be cut or folded. Printers also need bleed if the magazine or book is thick because they need to adjust the "creep"; pages are not cut exactly at the same exact width on thicker magazine or book, otherwise the pages in the middle would look wider than the pages that are closer to the covers.

A commercial printer can not print right to the edge of a sheet of paper. In other words, there's really no such thing as "borderless" printing on a commercial press. In order to combat this, you print a little over the edge of the design on larger stock (paper). This is called a bleed.

If you have content that you want to be right at the edge of a design (or just go off the edge), you must use a bleed. What a bleed does is extend the content beyond the paper edge. This way when the piece is printed then cut down to size, the cut chops off the extra (bleed) allowing content to appear to sit right at the edge of a printed piece (or trail off of it).

Essentially, if you have anything that goes beyond the edge of a printed piece, that item should bleed. It can be on one side of a page, two sides, three sides, or all four. These are commonly referred to as "quarter", "half", "three-quarters", and "full" bleeds.

With anything large format, it's prudent to ask the printer how much bleed they require; it's often in excess of 0.5". This is especially true if it's going to be mounted. Dry mounting a 8'x 4' duratran on perspex with only 2mm bleed is no joke. And there have been numerous occasions where I've rejected entire rolls of print because someone in pre-press decided you only need 0.25" bleed for wrap-mounted prints on 0.5" panels.

If the finished product is intended to have color bleed to the edge of the substrate without any white/unprinted/uncovered material, it requires a bleed to be included in the art for print production. The bleed allows for error in finishing. The bleed size should be determined by the expected quality, difficulty of the finishing required, precision and set-up of the equipment used to finish. The finishing department should be consulted when determining the required bleed.

In any case, if you are not sure what is required to ask someone who is. You will have the best shot at getting the finished product as expected. There is a lot of fudging things because the project was started without the finish in mind....ask the finishers!

Bleeds, Margins, live area... I think I heard something about those things all working together somehow in some mythical alignment of the Planets and Moon's...Customer art is shart. Train your in house designers and if a customer's art does not meet your requirements you have to express the possible quality issues and train them a little also.

Even after the the bleed air leak has been secured using the appropriate electronic centralized aircraft monitor (ECAM), quick reference handbook (QRH) or aircraft flight manual (AFM) procedure, secondary effects of the original fault may occur. Isolating part of the bleed air system will inevitably lead to some degradation in the operation of other aircraft systems such as:

Managing the remainder of the flight with the loss of some or all of these systems will require careful thought and planning. Having a comprehensive knowledge of the pneumatic systems will help in the decision-making process. It is essential that the pilots understand what is working and what is not, as well as the consequent limitations to the operation.

Some combination of gauges and warning systems is incorporated into the bleed air system to allow the pilots to monitor the normal function of the system and to provide audio and/or visual warning in the event of an overheat or failure. Valves are incorporated into the system to provide the means to automatically or manually isolate parts of the bleed air manifold or individual components in the event of a failure. Some of these defences include:

The electronic and mechanical defences, as listed above, are essential to the timely detection and successful containment of a bleed air leak. However, many emergency or abnormal checklists for bleed air faults require some post-action analysis to assess whether the action taken has been successful. A critical part of that analysis is a sound understanding, by the pilots, of the pneumatic system and all of its associated functions and components. If the isolation has not been successful, diversion should be initiated and an appropriate balance struck between the time spent on analysis and the need to get the aircraft on the ground as quickly as possible. Even when the isolation is successful, the pilots need to consider how the failure will affect the remainder of the flight. The impact of the loss of all or part of the bleed air system as it affects their particular aircraft type must be examined. Depending upon aircraft type, the analysis might consider items such as:

Aircraft wiring is often routed in proximity to pneumatic ducts. A bleed air leak from a compromised duct can melt the insulation of these wires, causing short circuits and potentially resulting in the generation of false warnings. These multiple warnings may mask the actual failure. If the bleed air leak is allowed to persist, heat damage to the airframe structure or a fire is possible.

F100, en-route, northwest of Goroka Papua New Guinea, 2020On 18 March 2020, a Fokker 100 en-route to Port Moresby experienced a failure of the cabin pressurisation and air conditioning system due to a complete failure of the bleed air system. An emergency descent and a PAN were declared and a diversion to Madang completed. The Investigation noted unscheduled work on the bleed air system had occurred prior to the departure of the flight and that long running problems with this system had not been satisfactorily resolved until after the investigated occurrence when four malfunctioning components had finally been systematically identified and replaced.

On 15 August 2018, a Boeing 737-300SF crew concerned about a small residual pressure in a bleed air system isolated after a fault occurred en-route then sought and were given non-standard further troubleshooting guidance by company maintenance which, when followed, led directly and indirectly to additional problems including successive incapacitation of both pilots and a MAYDAY diversion. The Investigation found that the aircraft concerned was carrying a number of relevant individually minor undetected defects which meant the initial crew response was not completely effective and prompted a request for in-flight assistance which was unnecessary and led to the further outcomes.

On 23 September 2019, the flight crew of an Airbus A320 on approach to London Heathrow detected strong acrid fumes on the flight deck and after donning oxygen masks completed the approach and landing, exited the runway and shut down on a taxiway. After removing their masks, one pilot became incapacitated and the other unwell and both were taken to hospital. The other occupants, all unaffected, were disembarked to buses. The very comprehensive investigation was unable to establish the origin of the fumes but did identify a number of circumstantial factors which corresponded to those identified in previous similar events.

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