146/Avro RJ engine anti-ice on ground
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146/Avro RJ engine anti-ice on ground
Hi folks,
Can anyone tell me why it (appears to be) standard procedure to have the engine anti-ice selected on before/during engine start on the 146/RJ?
Cheers all
Can anyone tell me why it (appears to be) standard procedure to have the engine anti-ice selected on before/during engine start on the 146/RJ?
Cheers all
The engine anti ice system is designed to be ‘fail safe’ - in the event of an electrical failure the valves will run to ‘open’ to ensure engine anti ice is always available. To keep the valves shut requires power, which generates heat. This reduces component life. Most operators will leave the AI selected on when on the ground, turning it off after engine start if not required for takeoff. There is a slight benefit to starting engines with it on (less back pressure?).
The MEL allows an engine AI to be inoperative, as it will be in the ‘safe’ position should icing be encountered. There is a temperature and performance limitation but this is not of great concern in most operations.
The MEL allows an engine AI to be inoperative, as it will be in the ‘safe’ position should icing be encountered. There is a temperature and performance limitation but this is not of great concern in most operations.
In non technical terms, compressor load during the start cycle is undesirable. Reduction in air load is achieved automatically by bleed band operation, but I assume every bit helps engine acceleration - the better to keep TGTs in limits. Engine anti ice air is a form of bleed air and therefore recommended until stable idle is achieved.
No doubt more technically savvy people will jump on here with more to add.
No doubt more technically savvy people will jump on here with more to add.
Last edited by Mach E Avelli; 16th Aug 2020 at 08:59.
CJ, Mach,
The discussion challenges an old and fragmented memory; 20yrs +
I do not recall any requirement to select engine anti ice on before engine start; switches were checked off during preflight checks.
A tech / sales pocketbook cira 1996 confirms the electrical description, but no procedural advice is given.
The bleed air discussion follows general theory, except for the 146 as below, and that bleed band is perhaps a 'red herring' during start.
The 'engine' anti ice system consists of two separate systems controlled by the same flight deck switch. The engine low pressure compressor anti icing, and the intake cowl. The front end compressor anti-icing uses air from the higher pressure compressor air (hotter later stages); the intake cowled taps the high temp combustor air (as for airframe anti icing).
During start the engine anti ice is automatically sequenced, as per the previous theory to off load the engine; vague recollections of lights coming on then off during start.
Were there any changes in procedure after the 'rollback' mods - 146 only; if so then the RJ should differ ?
The discussion challenges an old and fragmented memory; 20yrs +
I do not recall any requirement to select engine anti ice on before engine start; switches were checked off during preflight checks.
A tech / sales pocketbook cira 1996 confirms the electrical description, but no procedural advice is given.
The bleed air discussion follows general theory, except for the 146 as below, and that bleed band is perhaps a 'red herring' during start.
The 'engine' anti ice system consists of two separate systems controlled by the same flight deck switch. The engine low pressure compressor anti icing, and the intake cowl. The front end compressor anti-icing uses air from the higher pressure compressor air (hotter later stages); the intake cowled taps the high temp combustor air (as for airframe anti icing).
During start the engine anti ice is automatically sequenced, as per the previous theory to off load the engine; vague recollections of lights coming on then off during start.
Were there any changes in procedure after the 'rollback' mods - 146 only; if so then the RJ should differ ?
I have an original US Air checklist from 1991 for the 146 and it required Engine A.I. to be selected ON (if not already on) after shutdown. The next mention of these switches is in the After Start checklist (OFF or ON as required) so the implication is that they remained on for the entire time when parked.
The current factory checklist says the much the same, but is more repetitive, just in case some well-intentioned but ill-informed engineer turns it off.
The current factory checklist says the much the same, but is more repetitive, just in case some well-intentioned but ill-informed engineer turns it off.
Mach, thank you, more damage to a bruised memory.
However, starting with Eng A/I on could challenge some of the previous theory. The aspects of compressor bleed would still hold, but what might be the effect of starting with the airframe A/I bleed open, air taken from the combustor ?
Residual sceptical thoughts continue; a bias - that US operators wrote their own checklist, but on the other hand the manufacturers checklist supports their view.
Also, why does the bleed need to open automatically during start if the valve is already open ?
However, starting with Eng A/I on could challenge some of the previous theory. The aspects of compressor bleed would still hold, but what might be the effect of starting with the airframe A/I bleed open, air taken from the combustor ?
Residual sceptical thoughts continue; a bias - that US operators wrote their own checklist, but on the other hand the manufacturers checklist supports their view.
Also, why does the bleed need to open automatically during start if the valve is already open ?
Presumably there is a balance between tapping off enough air to offload the compressors and ensuring the right amount to safely support combustion.
Selecting airframe anti ice on during ground operation is not allowed. My theory: As well as the potential for engine over temps due insufficient airflow there is the possibility that wing and tail ducting/leading edges would be cooked due lack of airflow over the external surfaces.
In any case, for airframe AI to operate you would require the separate ENG AIR switches or APU AIR to be selected on, and would get a bunch of low pressure warnings until engines were advanced to power well above idle. All air switching is required to be off during start.
Re which way the bleed bands move and when, I think 'fail safe' - in flight you don't want to be losing bleed air if something goes wrong.
The reverse logic applies to engine AI - you want it to be there in flight to cover worst case situation. Airframe AI valves fail in position selected (I think - not having the books open - but it would be typical design of the day).
As for why all start sequence switching is not done automatically to 'pilot proof' the aircraft, it is after all a very old design not far removed from the day when the Flight Engineer took care of all these technicalities.
US Air was a very early customer and had quite a substantial Bae146 operation. I did my initial training with them and was quite impressed with how practical they were. Checklists and SOPs were quite concise but seemed to cover most contingencies. The original manufacturer documentation was also quite concise, but over the years it ‘grew like Topsy’ probably to satisfy entry into EASA Land.
Selecting airframe anti ice on during ground operation is not allowed. My theory: As well as the potential for engine over temps due insufficient airflow there is the possibility that wing and tail ducting/leading edges would be cooked due lack of airflow over the external surfaces.
In any case, for airframe AI to operate you would require the separate ENG AIR switches or APU AIR to be selected on, and would get a bunch of low pressure warnings until engines were advanced to power well above idle. All air switching is required to be off during start.
Re which way the bleed bands move and when, I think 'fail safe' - in flight you don't want to be losing bleed air if something goes wrong.
The reverse logic applies to engine AI - you want it to be there in flight to cover worst case situation. Airframe AI valves fail in position selected (I think - not having the books open - but it would be typical design of the day).
As for why all start sequence switching is not done automatically to 'pilot proof' the aircraft, it is after all a very old design not far removed from the day when the Flight Engineer took care of all these technicalities.
US Air was a very early customer and had quite a substantial Bae146 operation. I did my initial training with them and was quite impressed with how practical they were. Checklists and SOPs were quite concise but seemed to cover most contingencies. The original manufacturer documentation was also quite concise, but over the years it ‘grew like Topsy’ probably to satisfy entry into EASA Land.
Last edited by Mach E Avelli; 19th Aug 2020 at 00:58. Reason: detail
