The circumstances of the accident appear similar to several incidents that occurred with BAe146 aircraft that suffered a rare form of engine icing. All of the 146 engines are now modified.

The rare circumstances involved an unusual form of icing (‘grauple’ / soft hail) associated with ‘very’ large Cbs (Cumulonimbus Clouds). The phenomenon was apparently unknown to the industry; the engine icing occurred in conditions outside of the regulation boundary ‘Appendix C’. I was associated with some of the research flying conducted in Panama – a bit close to Venezuela !

One of the first BAe146 incidents occurred in Australia (at Meekatharra in WA); although ATSB investigated the ‘three engine malfunction’, their report was limited by the knowledge available at that time.

I investigated a later incident in Borneo which was similar to the MD-80 accident.

The 146 engines' N1 / N2 slowly ‘rolled’ back whilst the EGT remained high and then over-temped. The engines were shut down by the crew (all four of them in Borneo !!!) - (crew culture? afraid of subsequent sacking/punishment, already thinking about covering it all up, not realizing how serious their predicament was?)

Yes, but including operator culture – dominant engineering and previous aircraft type experience where an over temp of a turbo prop was ‘doom / death / destruction’.

The mechanics of the icing problem was due to low-temp or no engine inlet anti-icing in ‘mixed phased’ icing conditions – a mixture of soft hail and super cooled water. The water ‘stuck’ / froze on impact with the engine inlet stators and acted as the glue to stick the relatively larger ice/hail particles, this built up and choked the engine inlet. My personal belief is that many engines are susceptible to this, but with small differences in anti-icing temps and larger sized engine components they do not suffer such serious events (the industry has a vast range of unexplained minor events, ‘coughs and splutters’ in icing).

The significant amounts of inlet icing did not clear immediately below the freezing level, often lumps would pass through and damage the engine. In the Borneo incident the first engine relit at 2,500 ft after a 30 min descent from FL310.

A radar plot of the last BAe146 event is attached (pdf file) It shows the track relative to the Cb. A significant feature of the phenomenon were the large distances from the storm centre that the hazard could be encountered. Crews thought they were safe, but they were not. A side effect of modern weather (soft hail is green or non reflective); the crew think that they are safe and thus fly closer to storms. Most of the 146 events occurred on non passenger flights / cargo, thus with no pax to think about - so did this change crew behaviour?

Many of the Bae146 incidents involved complex human factors originating from surprise, stress, failure (inability) to think in unforeseen / non SOP conditions. They perhaps reflected a lack of basic airmanship and human limitations.

My interests in retirement remain with flight safety and I contribute voluntarily to FSF and other initiatives.

I am currently working on Human Factors projects.

Regards

al5071h

Something that I contributed to previously: http://www.flightsafety.org/ppt/managing_threat.ppt

		REFERS to this link
The circumstances of the accident appear similar to several incidents that occurred with BAe146 aircraft that suffered a rare form of engine icing. All of the 146 engines are now modified. The rare circumstances involved an unusual form of icing (‘grauple’ / soft hail) associated with ‘very’ large Cbs (Cumulonimbus Clouds). The phenomenon was apparently unknown to the industry; the engine icing occurred in conditions outside of the regulation boundary ‘Appendix C’. I was associated with some of the research flying conducted in Panama – a bit close to Venezuela ! One of the first BAe146 incidents occurred in Australia (at Meekatharra in WA); although ATSB investigated the ‘three engine malfunction’, their report was limited by the knowledge available at that time. I investigated a later incident in Borneo which was similar to the MD-80 accident. The 146 engines' N1 / N2 slowly ‘rolled’ back whilst the EGT remained high and then over-temped. The engines were shut down by the crew (all four of them in Borneo !!!) - (crew culture? afraid of subsequent sacking/punishment, already thinking about covering it all up, not realizing how serious their predicament was?) Yes, but including operator culture – dominant engineering and previous aircraft type experience where an over temp of a turbo prop was ‘doom / death / destruction’. The mechanics of the icing problem was due to low-temp or no engine inlet anti-icing in ‘mixed phased’ icing conditions – a mixture of soft hail and super cooled water. The water ‘stuck’ / froze on impact with the engine inlet stators and acted as the glue to stick the relatively larger ice/hail particles, this built up and choked the engine inlet. My personal belief is that many engines are susceptible to this, but with small differences in anti-icing temps and larger sized engine components they do not suffer such serious events (the industry has a vast range of unexplained minor events, ‘coughs and splutters’ in icing). The significant amounts of inlet icing did not clear immediately below the freezing level, often lumps would pass through and damage the engine. In the Borneo incident the first engine relit at 2,500 ft after a 30 min descent from FL310. A radar plot of the last BAe146 event is attached (pdf file) It shows the track relative to the Cb. A significant feature of the phenomenon were the large distances from the storm centre that the hazard could be encountered. Crews thought they were safe, but they were not. A side effect of modern weather (soft hail is green or non reflective); the crew think that they are safe and thus fly closer to storms. Most of the 146 events occurred on non passenger flights / cargo, thus with no pax to think about - so did this change crew behaviour? Many of the Bae146 incidents involved complex human factors originating from surprise, stress, failure (inability) to think in unforeseen / non SOP conditions. They perhaps reflected a lack of basic airmanship and human limitations. My interests in retirement remain with flight safety and I contribute voluntarily to FSF and other initiatives. I am currently working on Human Factors projects. Regards al5071h Something that I contributed to previously: http://www.flightsafety.org/ppt/managing_threat.ppt