DURING THE COURSE OF my 3500 flying hours (nearly 2000 of them in the aircraft at right), I easily spent just as many hours on the tarmac, sometimes under the shade of my aircraft's wings, as maintenance crews tried to figure out what had happened to one of the four aircraft engines. On one occasion, I had an ash encounter and on several other occasions I had fodded out (damaged an engine through Foreign Object Damage) one or more engines with something abrasive like a bird, a palm frond or a big lump of compacted snow. Through the course of my accident-free flying career, I learned you don't want to keep flying after those kinds of incidents and my judgment later became part of a body of work I accomplished as a flight safety officer, instructor aircraft commander during the Global Atmospheric Research Project, Air Staff planner and airlift control centre duty officer. I'm thinking about these experiences as people ask me about a persistent Icelandic volcano that seems to produce an especially abrasive ash that the jet stream carries over much of European flight paths. The ash cloud is impacting the travels of several people I follow on Twitter. I'm writing this short blog post as I tweet them from my Topgold account and listen to an Air Traffic Control audio excerpt with a Thomas Cook 757 flight that encountered ash cloud residue yesterday. Aircraft G-JMCF was on a positioning flight as TCX952P, returned to Manchester due to a loss of compressor bleed air from one engine after crew sensed an "intense smell of volcanic ash" during the climb between FL160-FL200. The aircraft was out over the North Sea off Nofolk/Suffolk.
In the Lockheed C-141 Starlifter, we could smell strange odors when we flew through unpure air. Volcanic ash could smell like sulfur or seem as acrid as burning electrical cable. It would make my eyes water. Neither smell is recommended when you're on the ground and in a closed pressurised compartment of an aircraft, it's not smart to bring contaminated air into the mix.
Staying ahead of where the cloud is moving means making continuous sampling flights. Those are terribly inefficient as I saw when we flew 10-hour equatorial circuits over the Pacific Ocean in the 80s. Nonetheless, air samples can provide exceptionally valuable data that calibrate the computer models which produce the plots I see on RTE and Sky News reports. Fixing model calculations with in situ airborne measurements maintains a sanity check on the computer model of the ash cloud.
Before we launched on our 10-hour air sampling missions, we had a pre-flight that took two hours and fifteen minutes. Post-flight data reduction was an overnight affair. You could not fathom doing this kind of real-time monitoring because at the end of the day, it's not real-time tracking.
The BA146 aircraft doing the current ash cloud tracking actually look like miniature C-141 aircraft. Those aircraft gather data that validate satellite imagery.
The news imagery I'm reviewing currently shows an Icelandic eruption plume that extends up to five kilometers high (actually 14-17,000 ft) but it sometimes shoots up to 6 km (20,000 ft). The plume has visited the west coast of Ireland but it's slowly decreasing as well as pulsating.
No computer model is going to give a reliable prediction on when the current Icelandic eruption will end. If I depended on tourism for my island, I'd start throttling back on some fixed expenses. And if I was a pilot, I'd wipe my compressor inlets with a white glove on pre-flight and post-flight.
BBC -- "Ryanair admits volcanic ash in Belfast engines" in a BBC report, 10 May 2010.
Boeing has issued Ash Cloud Flight Guidance [2.6 MB PDF]
Previously: "Notes on Flying through Volcanic Ash", May 2010.
Direct link to MP3: http://www.insideview.ie/files/ash_cloud.mp3