[opendtv] Off topic: volcanic ash effects

From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
To: "opendtv@xxxxxxxxxxxxx" <opendtv@xxxxxxxxxxxxx>
Date: Mon, 19 Apr 2010 16:02:05 -0500
This is an excerpt from a NASA report. It shows the extent of damage if an 
airliner flies through ash, even in what appears at first to be relatively mild 
conditions.

----------------------------
NASA/TM-2003-212030
Engine Damage to a NASA DC-8-72 Airplane From a High-Altitude Encounter With a 
Diffuse Volcanic Ash Cloud
August 2003

Thomas J. Grindle
NASA Dryden Flight Research Center
Edwards, California

Frank W. Burcham, Jr.
Analytical Services and Materials, Inc.
Edwards, California

[ ... ]

From the Summary section:

In the early morning hours of February 28, 2000, the National Aeronautics and 
Space Administration (NASA)DC-8 Airborne Sciences research airplane 
inadvertently flew through a diffuse plume of volcanic ash from the Mt. Hekla 
volcano. There were no indications to the flight crew, but sensitive onboard 
instruments detected the 35-hr-old ash plume. Upon landing there was no visible 
damage to the airplane or engine first-stage fan blades; later borescope 
inspection of the engines revealed clogged turbine cooling air passages.

[ ... ]

ENGINE OVERHAUL RESULTS

All four engines were sent to the General Electric Strouther overhaul facility 
near Arkansas City, Kansas. Photographs were taken as the engines were 
disassembled. All engines exhibited a fine white powder coating throughout. 
There was leading edge erosion on HPT vanes and blades, blocked cooling air 
holes, blistered coatings, and a buildup of fine ash inside passages. Serial 
number 692632 (the number four engine on the DC-8) had the most severe damage; 
this may be partially due to the older hardware still resident in this engine. 
Figure 11 shows photos of the damaged HPT blades, with clogged cooling air 
holes, leading edge erosion, buildup of ash in passages, and blistered blade 
coatings clearly visible. Total cost of refurbishment (to standard flight 
condition) for all four engines was $3.2 million.

Even though this was a diffuse ash cloud, the exposure was long enough and 
engine temperatures were high enough that engine hot section blades and vanes 
were coated and cooling air passages were partially or completely blocked. The 
uncooled blades still performed aerodynamically but necessitated expensive 
overhauls. The insidious nature of this encounter and the resulting damage was 
such that engine trending did not reveal a problem, yet hot section parts may 
have begun to fail (through blade erosion) if flown another 100 hr.
---------------------------

So, even though I see a comments about airlines being willing to compromise 
"safety," it seems to me that airlines would hardly be willing to submit 
themselves to engine overhauls at 100 hour intervals, or less, just to rush 
planes back in the sky.

Bert
 
 
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[opendtv] Off topic: volcanic ash effects

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