(Information for airline operators of CF34-3 engines. Published by GE Aircraft Engines Commercial Product Support.)
TO: All Canadair Regional (100/200) Jet Pilots No. 11 Revision 1
SUBJECT: Operation Below 78% N2 in Icing Conditions Date: 14 APR 1998
The CRJ EICAS N2 gage displays an amber/ yellow band below 78% N2 whenever the wing anti-ice protection system is activated. If N2 is reduced below 78%, it is annunciated as a caution by turning the pointer and display digits amber/yellow.
The threshold of 78% N2 was determined by Canadair in testing to show the level above which anti-icing was fully effective under all conditions up through “continuous maximum icing”. Thus at conditions that are less severe, the engine may be operated at settings below 78% N2.
If power settings below 78% are used, for aircraft operational considerations, monitor the CAS Amber Caution messages for L(R ) Wing Anti-Ice, or L(R ) Cowl Anti-Ice. The L(R ) Wing Anti-Ice message will illuminate if there is insufficient heat at the wing leading edge or if there is insufficient duct pressure. The L(R ) Cowl Anti-Ice message will illuminate if there is insufficient pressure in the engine inlet cowl anti-ice duct when the system is turned on.
Assuming that the ice protection system is functioning properly, operating below 78% N2 is acceptable as long as the Wing or Cowl Anti-Ice Caution messages do not annunciate. If this does occur, the recommendation is to advance engine thrust levers to greater than 78% N2 to allow higher bleed air pressure to raise the wing leading edge temperature above the sufficient heat level. This condition was simulated by Canadair in “Delayed TURN ON” tests where ice build up was cleared by activation of the system after a 30 second delay. Following a period of dwell at greater than 78% N2, the engines may be reset lower. If lower settings resulted in Wing or Cowl Anti-Ice messages to annunciate, a slightly higher setting (closer to 78% N2) should be used to decrease the probability of illuminating these messages.
Engine N1 vibrations may indicate the accretion of ice on the fan spinner in icing conditions over observed steady state levels. This secondary indication may be used as additional information regarding the severity of icing conditions and, therefore, be used to maintain higher N2 power settings.
In summary, the EICAS N2 amber/yellow indication band is a conservative range that is intended to provide a minimum power setting at which the ice protection system is fully effective in all icing conditions, and also allows an acceptable descent rate for the lowest weight aircraft while avoiding nuisance Anti-Ice caution messages. In the event that higher descent rates are needed, for operational reasons, lower power settings may be used if the severity of icing conditions permit. Proper system operation can be effectively monitored by using the Wing Anti-Ice and Cowl Anti-Ice messages to alert the pilot of insufficient heat to the wing leading edge or the cowl.
This recommendation has been jointly reviewed by Canadair and GE Aircraft Engines. Please contact us if there are any further questions regarding this subject.
