Good to have you back here again Howie 
Really alternate side Ignitors? All RR aero engines I have worked on always sparked up both sides every time, well the Avon, Spey 202, RB199 & the Oly 20202 (Vulcan) and industrial Oly did. Would this have made a difficulty with starting logic?? Was there LH & RH Ignition selector switch maybe?
There was no automatic ignition selection logic as such built into the start sequence, but a manually selected L & R ignition selector switch. The reason of course to alternate L & R selection during starting was to detect otherwise dormant ignition failures if 'BOTH' was always selected. (Modern A/C with AUTOSTART do not have this problem, if an ignitor fails during the engine start sequence the other is automatically selected and an ignition status message is set on the lower EICAS screen). The ignition L/R selector switch was bypassed during engine operation by the auto-ignition system, where if the engine control unit detected a flame out (set at 58% N2) both ignitors would automatically fire up. The sequence would release onece the perceived N2 rose above 63%. The ignition system had several reliability issues, the first was the plugs themselves. Penetration into the 'can' was crucial; if it were more than about 130 thou', the tip would very quickly burn off. We soon learned that a penetration check was vital when fitting a plug and shims needed to be used to get the correct penetration. The other reliability issue was the ignition leads themselves; For the first 10 years of service they were a major pain until 'they' (Rolls-Royce) finally got it right. Also until Rolls modified the lead clipping, it could take 3 to 4 HOURS to change a lead. The dual channel HEIU itself was as good as gold, and seldom let us down, It was a very powerful 8 Joule 2KV beast, and you obviously treated it with utmost respect.
Best regards
Dude 
Last edited by M2dude; 18th Jan 2011 at 06:28.