Classic B747 - Electrical relationship between Ignition & Engine anti-ice!
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Classic B747 - Electrical relationship between Ignition & Engine anti-ice!
Why, when we have a 'no light-off' with one of the two ignition systems during ground start, and the FE then uses the other ignition to light it off, does he then check that the engine anti-ice still works on that same engine, as per the MEL?. .Just curious,. .Cheers
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To be sure that the engine doesn't go quiet in icing conditions and need an in-flight re-start. With a less than perfect ignition system. Or something like that. <img border="0" title="" alt="[Eek!]" src="eek.gif" /> . .. .Was it really wise getting rid of all those Flight Engineers? . .. .**********************************. .Through difficulties to the cinema
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Thanks Blacksheep, but as far as I am aware, only one ignition is required when anti-ice is switched on, and only remains on for a short while, if their is only little turbulence.. .. .I sort of thought that there must be some sort of electrical commonality in the operation of the two systems, and the a/i check just proves that the problem is with the igniter plug giving up, rather than the common control system.. .Sounds reasonable, but can't find anything in writing, and the groundies can't tell me.. .I got this info from an FE, that's why it sounds reasonable!. .Any more ideas?
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"but as far as I am aware, only one ignition is required when anti-ice is switched on, and only. .remains on for a short while, if there is only little turbulence.". .. .G'day, FD. .Are you referring to the sort of Anti-ice system which fires up the ignitors automatically for about 60 seconds to prevent a flameout due to Anti-Ice melted ice (i.e. ice which may have formed previously in your engine inlet)? . .. .Perhaps Blacksheep is more concerned about preventative or long term use of the Anti-Ice System, i.e. to stop the ice build up in the first place and keep the engines ice free. I believe that ice, if left to accumulate in an engine intake over a long period in the absence of anti-ice may snuff out the engine irrespective of whether the ice was melting or not (due to disrupted airflow in the inlet).. .. .In your situation, if the engine should flame out, due to the build up of ice or the melting of ice, you only have half the capacity to relight the engine. If there is no ice build up in the first place (say because you predicted that there would be ice ahead and switched on the Anti-Ice system beforehand manually), the engine would be less likely to flame out under icing conditions (and you wouldn't need to restart the engine with a single ignitor).. .. .Hope this makes sense.. .. .Rgds.. .Q.
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mustafagander Just checked 3 mel's for RR, GE and Pratt all say 8 installed 4 required, all for classic, it is slightly different for the 747-400 where you can still have 4 inop but must have ignition 1 on at least 2 engines. 
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Hi all,
We seem to have gotten off the original track just a bit!
In a Classic, with one ignition on one engine inop, (if both were inop, we woundn't be able to start the engine), we are required to test that the same engines' anti-ice system still remains serviceable - my question is why that is so, since there is seamingly no direct relationship.
Thankfully, the Classic is fully manual, and as such, only does what you tell it to do, when you tell it to do it!!
Yes, we do always use two ignitions for t/o and landing, and one ignition, (the working one, hopefully!), when we initially select nacelle anti-ice in crz, and if the ride remains smooth, that ignition is turned off.
My original question still stands, anybody know?
We seem to have gotten off the original track just a bit!
In a Classic, with one ignition on one engine inop, (if both were inop, we woundn't be able to start the engine), we are required to test that the same engines' anti-ice system still remains serviceable - my question is why that is so, since there is seamingly no direct relationship.
Thankfully, the Classic is fully manual, and as such, only does what you tell it to do, when you tell it to do it!!
Yes, we do always use two ignitions for t/o and landing, and one ignition, (the working one, hopefully!), when we initially select nacelle anti-ice in crz, and if the ride remains smooth, that ignition is turned off.
My original question still stands, anybody know?
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Is this a JT9D powered Classic, or one of those "bastardized" versions? If its a JT9D, the only connection that comes to mind would be to ensure that either start switch electrical system, and thus its associated ignition, doesn't have some fault that prevents the pylon valve or high stage valve from functioning correctly. The Nac A/I valve is electrically actuated, air operated. Potentially then, the Nac A/i valve might not get sufficient flow and temp air for de-ice / anti-ice for Take-off if either valve's stuck somewhere they shouldn't be. When you dexterously advance the throttles,the high stage closes and the core engine provides all the air. That said,the high-stage and pylon valve lights should clue you to these failure modes. It's weak but it's all I got..............
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Thanks 'Tinyrice',
I'm sure I don't know what you mean by those "barstardised ones', this is also required on the RR powered aircraft, incl the C2 and D4 series, as well as the PW ones, that's the -7 series, incl. the 7R4G2 engines, can't remember offhand if it's the same for the GE CF6-50 and -80 engines, havn't seen one for awhile!
We always use the 'packs off' technique for t/o, and as such, the pylon valves are cycling, with nothing really to supply, until the first pack is selected at around 300', and as for the high stage valves, those lights should be out before power is stabilized, prior to advancing power for t/o!
Many thanks, but I'll keep looking.
Cheers.
I'm sure I don't know what you mean by those "barstardised ones', this is also required on the RR powered aircraft, incl the C2 and D4 series, as well as the PW ones, that's the -7 series, incl. the 7R4G2 engines, can't remember offhand if it's the same for the GE CF6-50 and -80 engines, havn't seen one for awhile!
We always use the 'packs off' technique for t/o, and as such, the pylon valves are cycling, with nothing really to supply, until the first pack is selected at around 300', and as for the high stage valves, those lights should be out before power is stabilized, prior to advancing power for t/o!
Many thanks, but I'll keep looking.
Cheers.
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Not sure if we're on the right track at all here...but here goes.
On some types of aircraft (Modern Boeings for sure) there are TWO ignition selectors (two igniters per engine).
Depending on the 'selected' position, and what systems use it, an 'inop' igniter (subtle or obvious) 'selected' will obviously be of no use.
We have procedures, albeit not the Classic 747, to select 'BOTH' AFTER engines started. We select one igniter (left) for east-bound flights and the other (two, right) for west-bound flights during pre-flight for engine start.
Should the engine fail to start due igniter failure, all is obvious.
Should the igniter fail after engine start, and if it is NOT in BOTH position, then crew WILL be unaware of the failure until the next time the engine is started with that igniter selected (unless there is a failure detection system - no EICAS mesage on our type of aircraft).
Anti-ice uses the 'selected' igniter on MOST aircraft.
If you select BOTH after engine start, the likelihood of both having failed without pilot knowledge, is remote (has happened), however, the remaining igniter WILL be available for Anti-ice usaeage.
Now, on the classic (of which I know nothing! - sadly born in a different generation), MAYBE the Anti-ice check served the same outcome.
A look into the systems of igniter (selected) VS. anti-ice might help understand the 'type' situation.
Hope this is helpful.
Here's to ice-free engines!
On some types of aircraft (Modern Boeings for sure) there are TWO ignition selectors (two igniters per engine).
Depending on the 'selected' position, and what systems use it, an 'inop' igniter (subtle or obvious) 'selected' will obviously be of no use.
We have procedures, albeit not the Classic 747, to select 'BOTH' AFTER engines started. We select one igniter (left) for east-bound flights and the other (two, right) for west-bound flights during pre-flight for engine start.
Should the engine fail to start due igniter failure, all is obvious.
Should the igniter fail after engine start, and if it is NOT in BOTH position, then crew WILL be unaware of the failure until the next time the engine is started with that igniter selected (unless there is a failure detection system - no EICAS mesage on our type of aircraft).
Anti-ice uses the 'selected' igniter on MOST aircraft.
If you select BOTH after engine start, the likelihood of both having failed without pilot knowledge, is remote (has happened), however, the remaining igniter WILL be available for Anti-ice usaeage.
Now, on the classic (of which I know nothing! - sadly born in a different generation), MAYBE the Anti-ice check served the same outcome.
A look into the systems of igniter (selected) VS. anti-ice might help understand the 'type' situation.
Hope this is helpful.
Here's to ice-free engines!
Last edited by safety_worker; 8th Apr 2002 at 19:35.
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Hmm, according to the CB panels (P6), there is no link up between the eclectrics of these two items, this is on GE-E's and JTD's, interesting observation this...needs a bright spark
