Bell 206b

[Nick]

ok, I've got my diagrams

 

 

So there's a mecanic pump : it's called "engine driven fuel pump" (my mistake) on the data product book and "high pressure fuel pump" in the FM.

 

The Engine high pressure fuel pump is either a dual element type pump or a single element pump. A failure of either element of the dual pump will not result in an engine failure....etc

 

So, how can you know that one of the element is down ? Less performance ? How do you read it on the panel ?

 

407too you're right : without engine driven pump, there's just the sound of wind in a 206; is it valid for all turbine helicopters or some models can fly just with boost pump as suggested by Cap ?

[Skids Up]

if you loose your engine driven fuel pump in a 206, your engine DOES go quiet

 

Have to agree with you 407 too, :up:

 

It was explained to me that the reason you are required to desend below 6000' with the loss of boost pump(s) is that above that altitude, the atmospheric pressure is not great enough to push down on the fuel hard enough to supply it to the engine driven pump.

 

but if you lose your engine driven pump, it doesn't matter what height you are at. You'll be on your way down quickly.... :shock:

[407 too]

nick, as i'm not an engineer or familiar with many types of turbines, i can only offer an assumption - which is that ALL turbines would require the engine driven fuel pump to be functional to run

 

as skids up has stated, boost pumps only give aide to the engine driven pump, they are great pushers, but not great suckers

(don't start in with the vaccum cleaner jokes)

[Phil Croucher]

The boost pumps are merely there to prevent cavitation, as with any jet engine, if one is supplied at all - otherwise it has the equivalent of a heart attack at altitude as the air bubbles out. Cap's right - the original 206 was supplied without a boost pump, then one was added, then another as a backup, which is why the fuel line goes from one to the other then the fuel valve, rather than both into the same point on one line.

 

The only indication of a boost pump failure in the cockpit is the warning light, and possibly a slight reduction in fuel pressure, if you are sharp-eyed enough to detect it. If one fails, you should descend below 6000 feet, as the man says, and the unuseable fuel becomes 10 US gallons, calculated on a level attitude, so no excessive movements or you will be sucking air!

 

As to whether one element of the engine driven pump has failed - I don't think there is any indication, but I could be wrong

 

To explode one urban myth - when you test the pumps individually, you are checking that the NRVs are working, rather than whether the pump is working. The NRV is there to stop fuel circulating back to the other pump.

 

Nick - if you hang on a couple of months I have a book on the Bell 206 just about to be published - all the information you should need for a decent conversion will be in it, without duplicating the flight manual (I'm a JAA DFTE)

 

Cap - the scottish wires are OK - it's the 11 Kv ones in Cornwall and Wales that are the crazy ones! One good thing about being below 50 feet is that the RAF jets are above you - any down that low have a severe problem!

 

phil

[cap]

407 too -----you are correct and my fingers didn't put down what I meant. I'm aware that if the fuel pump goes on ANYTHING you got silence. What I was meaning to say was that if the fuel pump goes into "bypass" for some reason, you still got the added pressure from the boost pumps. Good eyes...thanks for that.

 

Further to what Albert has stated, what the boost pumps can also do is "mask" an air leak of the A/F Fuel filter. If you have one sucking air, then you'll quickly confirm whether that is true by trying a start WITHOUT the boost pumps engaged. If such is the case, she will "sign-off" around 45-55% N1. If she is sucking air in that way, one will probably have problems at some point with the govenor and will usually be indicated many times by the N2 not maintaining 100%, but have a tendency to "search" in many modes of flight or not resume it's previous setting on start-up.

 

From my beginnings on the 206A Model, the instructions from Bell and engineers on using boost pumps has gone through many changes and they were:

 

1) One boost pump pushed engaged.

2) One boost pump engaged, but you were instructed to make that boost pump the rear one.

3) Two boost pumps and NEVER use one.

 

So I've gone from no mention at all of boost pumps by Bell, to being told to use one, then being told to use two........and EACH time Bell advised that was the way to do it. It would appear to this humble person that Bell was therefore wrong on two of those occasions......take your pick. One thing remained the same over all those years......don't "screw around" above 6000' without.

 

Albert.......11Kv?.......you must be kidding. I'm used to hearing numbers like 138kv or 500kv. What's the Amps on a line like that......any idea? I'll assume those lines are poles and not towers....or am I wrong? You got some respectable rock piles in Wales too, so that must make for some "interesting" line patrols?

[Phil Croucher]

Here's an 11 kv line - they go off in spurs all over the place:

 

 

Don't even think of doing stuff like this in a 300 or a robbo - even a 206 struggles in some areas

 

phil

[ray]

The Bell 206 used to have an 'impending bypass light' for the engine driven fuel pump.

There used to be a pressure switch measuring the difference in pressure 'before filter' and pressure 'after filter'.

I don't recall the numbers, but if the pressure differential got too high, a light came on in the cockpit telling you your engine driven fuel pump filter was clogging up.

 

The 206 now has an airframe mounted fuel filter between the fuel boost pump and the engine driven fuel pump.

This airframe fuel filter has a bypass light indicator switch built in.

Because the filter is before the fuel pump, it will clog up before the engine driven fuel pump filter.

 

So there is a bulletin that allows you to remove the differential pressure switch off the engine driven pump if there is an airframe filter installed with a light switch.

 

For Bell 206's that regularly fly over 5000', there is a modification that should be carried out on the boost pump cartridge. It is a TB to replace the bypass 'umbrella' on the top of the housing.

[Nick]

Good info :up:

 

Is there still some 206 without A/F fuel filter ? Is the filter easy to clean in the field or is it an AME job ?

 

What's the procedure after a flight with a fuel filter bypassed ? How can you judge if the engine was damaged ?

 

I heard about a new procedure in case of "fuel pump" warning light. In my FM it's just "descend below 6000ft", no recycling of breakers...still current ?

 

yessss againnnn stupid questions

 

 

Mr Ross, I'm waiting for your book !

[cap]

Nick ----there's no "stupid questions".........only "stupid answers".

 

A clogged engine driven fuel pump on a 206 that goes into "by-pass" mode won't cause any damge unless the "loose link between the collective and the cyclic" decides to fly around and ignore it. It means the a/c is telling him/her something about the fuel system and he/she best pay attention. He/she may have got their hands on some bad fuel for example. It's an AME's job to rectify that problem with the fuel filter by the way and if the pilot flies around all day after getting that light, he'll have the engineer shaking his head too.

[Phil Croucher]

One curious thing about the airframe filter is that, if it is fitted, you don't need anti-icing additive - haven't figured out why, yet!

 

Phil