Dear Oluf,
I newer flew with RR engines, but my P & Ws on a MD-80 once had a very hard time getting up in RPMs with the front end of the engine all iced-up, it first "hesitated" then started to stall, first after three tries and very slow advancement of the throttles it worked normal again. (Eng. Anti-ice was ON)
Was what you describe here on the ground while taxying or in flight?
I remember an accident which was caused by moderate icing, engine vibration and consequent failure of the icing panels on both engines.
Quoting from the report:
"Conduct of flight:
Simultaneously with the icing alert the crew switched the engine ant-icing and airframe anti-icing systems on. The crew attributed the increased vibrations indicated for the RH engine, after reduction of airspeed and entering cloud (icing conditions) in FL100, to ice formation on the fan. The airplane flew, for approx. 6 minutes, with reduced engine thrust under moderate icing conditions which, in all likelyhood, led to icing of the fan blades of both engines.
After a prolonged time under moderate icing conditions and low engine thrust, ice developed on the rotors of the low pressure compressors of both engines. During descent from FL90 to 3,500 ft the engines were running smoothly in a low thrust range and all engine indications were in the normal range. The crew could not recognise the reduced performance of the two engines. Thus the PIC did not hesitate to operate the airbrakes for some time, in order to reduce the airspeed to such a degree that the flaps could be extended. Once flaps and landing gear were extended it became apparent that the engines developed insufficient thrust. There was no malfunction indication at that time because in the flight warning computer monitoring of the N1 to EPR ratio is not intended.
EPR indications showed, however, that dispite an RPM increase the engines developed insufficient thrust.
Cause:
The bonded joints of the ice impact panels on both engines failed
due to strains caused by ice-induced vibration of the engines and by ice which had detached from the rotors of the low pressure compressor. The loose ice impact panels became trapped in front of the outlet guide vanes of the low pressure compressor and affected the airflow in the by-pass duct in such a way that the engines only produced low thrust."
Now compared to BA38, in the above mentioned case RPM (and EGT) increased but the engines developed insufficient thrust due to air flow restrictions.
Increase in RPM and EGT implies that the fuel flow was getting to the engines.
In case of BA38, thrust increased initially, then rolled back even with fully opened fuel metering valves.
After the rollback, no mention of increased RPM or EGT, indicating this is not very likely to be an icing problem but that the required fuel flow was not getting to the engines. What is also missing in case of BA38 is that no mention has been made of vibration due to icing or shedding of ice.
For the full report, here is the link (including FDR data, please note RPM, EPR and EGT parameters):
http://www.bfu-web.de/nn_53140/EN/Pu...MUC_Fokker.pdf
Green-dot