Just_a_fan wrote:WhiteBlue wrote:
There are obviously sensible people holding different opinions or we would not have had a bunch of successful flights. There must be levels that are tolerable.
Aircraft engine suppliers do not tolerate sea water in turbines. Nevertheless there are applications which simply use them in sea water contaminated environments and manage the consequences.
On the BBC Radio 4 programme this morning there was a discussion along the lines of: the manufacturers have been tasked with assessing damage to engines etc. and coming up with safe tolerances. These new tolerances are higher than the previous ones. Thus, they are able to fly in areas with more ash than before.
The tolerances are still pretty fine but they are coarser than before.
The discussion in Germany has advanced to the conclusion that the closure of the national airspace was not necessary. It was the result of lack of data. Nobody knew the concentration of ash in the air and nobody had any informations on critical concentrations for aircraft operations. The only thing we know for certain is that we erred to the side of caution and caused all this disruption unnecessarily.
Apparently the criticality of Volcano ashes is derived from experiences such as
KLM Flight 867 on December 1989 when the Jumbo 747 flew into the cloud of Mount Redoubt. Volcanic ash melts when it gets into jet engines. The molten silica coats the inside of the engine with glass, which confuses sensitive engine monitoring equipment. Safety equipment is fooled into thinking the engine is overheating, and an automatic shutdown begins. An alert pilot flying at a high enough altitude can safely restart the engines - as KLM 867 did - but a pilot flying at low elevations might not have enough time to save the airplane.
Nobody knows which ash concentration was present when the incident occurred and so people just plugged some figures out of the air. The critical concentration may have been thousand times higher than the one measured over Germany in the last five days. We do not know this. All we know is that the concentrations measured by the LIDAR equipped DLR flight on Monday was subcritical as proven by numerous flights conducted during the day.
Another important issue is the detectability of ash clouds. The ash doesn't polarize like water fog hence the ash cannot be detected by RADAR. Only laser based LIDAR detection systems are capable of analyzing ash concentrations in clouds.
Looking back on the economic damage of this experience (with cost estimated upwards of 2 billion €) there is little doubt that aircraft manufacturers need to do research with LIDAR equipped planes to establish critical conditions that can lead to shut down of engines. It can also be argued that at least a certain percentage of planes need to be equipped with LIDAR to quickly collect data in case another eruption occurs close to heavily travelled air space.
At the moment the air space over Germany is fully released to traffic and all closures are now cancelled. It will take the airlines days to get up to full schedules again. Today Lufthansa will run 500 of 1800 connections. It may take another 3 or 4 days until the full schedule resumes.
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