Effects of Volcanic Ash Cloud on Pitot/Static systems?

[Neupielot]

Hi all. Are the pitot /static systems affected at all by the ash cloud? Since airlines are now pushing to resume service across europe it seems. Sorry if its a noob question. I'm just wondering if the aircraft pitot/static systems will be affected if flying through ash cloud for months ( and months?).

Thanks.

[Captain Smithy]

I would imagine that if the concentration of ash is high enough then yes there may be some chance of pitot blockage.

Might be an interesting thing to watch for over the coming weeks for those who fly at higher altitudes...

Have heard many stories of all sorts of foreign matter causing blockages, e.g. insects, mud, dust & dirt, blades of grass (!) etc.

Smithy

[Neupielot]

Thx. Engine failure is serious....pitot/static blockages flying at night is a total nightmare. Time to go on leave. Someone plug that volcano plz!

[muduckace]

I would imagine pitot blockage is a possibility, all information I understand on the subject is that engine failure would occur first.

[Self Loading Freight]

Certification regime for ash tolerant aircraft

Having watched all this kerfuffle, which like the volcano itself is spewing forth a variable mixture of light, heat and crud of differing penetrability, I wonder what the ideal long-term outcome is.

It strikes me that the major problem is lack of definition of the problem. We do not know, except for a few datapoints, how airframes, systems and engines behave in volcano-contanimated air. Particulates and corrosive gases are not part of any certification regime. So, the questions are:

1. Is a total-avoidance reaction the most cost-effective? It's been a costly and frustrating exercise on this occasion, but if it's only going to happen once in a hundred years then the costs and frustration may be worthwhile.

2. If not, what do we certify for? What is the expected range of contaminants that may be encountered, and what within that range can be designed against?

A parallel may be the weather, where we have characterised a wide range of conditions and built systems that can be certified to work within a subset of those conditions. Aircraft carry sensors that allow pilots to make decisions on local data; ATC have access to more data and there are copious ways to create and apply a big picture that makes constant cost/benefit/risk analyses.

It's certainly feasible, these days, to imagine sensors both airborne and ground/space based that constantly check for a wide range of contaminants, and to have engines, airframes, etc, that are certified for operation under certain contaminated conditions. Such things would doubtless have reduced Eric Moody's value as an after-dinner speaker and would increase the burden of training and qualifying pilots, but neither is necessarily a deal breaker.

However, the overall costs of such a regime would be very large, it would take decades to implement, and like any extra layer of complexity would carry risks of its own. It would also create quite a lot of economic activity, which us SLF would doubtless bear... ah, well.

Would it be worth it? How can we tell?

[Checkboard]

We do not know, except for a few datapoints, how airframes, systems and engines behave in volcano-contanimated air.

Unfortunately we DO know. here is a research paper/investigation from a NASA instrumented air quality test aircraft which inadvertently flew through the edges of a volcanic cloud:

http://www.alpa.org/portals/alpa/vol...8AshDamage.pdf


Note the following from the report:

The flight crew noted no change in cockpit readings, no St. Elmo’s fire, no odor or smoke, and no change in engine instruments. They did notice that no stars were visible, but this is typical of flight through high cirrus clouds.

After landing in Kiruna, the engine oil, oil filters, and heat exchanger filters were removed and saved for analysis. Visual inspection of the airplane and first-stage engine fan blades showed no apparent damage or erosion on any parts of the airplane, nor was any ash found in the engine cowlings or other normal access panels. Borescope inspection equipment was not available in Kiruna, and since there was no detected change in engine performance, the research flights continued.

the airplane was ferried back to Edwards. A total of 68 flight hours had accumulated since the ash encounter. At Edwards, engine borescope inspections revealed clogged cooling passages and some heat distress in the high temperature section of the engines. Engine number four appeared to be the most heavily damaged and was removed. Following the number four engine teardown and inspection, the other three remaining engines were also removed and disassembled for inspection.

There is no evidence of significant engine performance change following the ash encounter. In fact, there does appear to be a slight drop in cruise EGT. This is consistent with experience that says that a very mild ash encounter cleans and polishes the compressor blades, slightly increasing their efficiency. Blocked turbine cooling air passages and holes would be expected to reduce HPC bleed flow, which would also slightly improve performance. The increased blade and vane metal temperatures would degrade their service life, but not their performance. A blade with blocked cooling operates at a sufficiently higher temperature so that its service life may be as little as 100 hr as compared to a normal service life of thousands of hours.

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 [seven minutes] 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.

[fredgrav]

I'm just wondering if the aircraft pitot/static systems will be affected if flying through ash cloud for months

Volcanic ash is made of very fine particles (down to 1 micron) that can even penetrate easily the most tightly sealed parts. A total blockage is a very extreme situation likely to happen while flying in the "ash" for hours ... nevertheless a relatively low quantity of volcanic ash may be sufficient to disrupt the flow of air in the probes, thus generating unreliable speed indications.

Suggest reading the following Airbus notes on Volcanic Ash Awareness:

http://www.airbus.com/fileadmin/medi..._ENV-SEQ06.pdf

Safe Landings,
fredgrav

[ggofpac]

The very first line of the Brief--> Flying through ash cloud should be avoided by ALL means.

I guess it wasn't safe before but then now if the airlines gonna go bankrupt they've taken a different view . Lawyers are all lined up ready to sue the minute the first accident happens.

[bluesafari]

checkerboard

Very interesting article, I suspect that the cost of flight through volcanic ash may not be truely felt for some time to come, but it will come when engines start to fail power assurance checks and have to be replaced, it is not clear that anyone really knows what the cloud consists of and the effect of those contaminants on hot turbines, particularly the Willie Walshes of this world ! Keep your eyes on those gauges!

[One Outsider]

Originally Posted by bluesafari

....when engines start to fail power assurance checks and have to be replaced......Keep your eyes on those gauges!

The point made in the report is that the damage done does not show in the engine parameters or performance. It will only show itself when a boroscope inspection is performed or when bits of the turbine starts flying off.

[lomapaseo]

The point made in the report is that the damage done does not show in the engine parameters or performance. It will only show itself when a boroscope inspection is performed or when bits of the turbine starts flying off.

The report is not an end-all, it only represents the knowledge of the day.

Engine trending over time can show up lots of things according to the model created.

I suspect that standard modeling of EGT and FF would show up the effects of blade erosion and time to refurbish more often.

OTOH I suspect that EGT margins and FF might actually improve if the stuff glassifies in the burner-turbine nozzle vanes this is often followed by engine surge-stalling at an inconvenient time.

Then again the nasty clogging of cooling holes in blades and vanes leads to metal deteoration which goes unseen in trending plots but is detectable by scheduled borescope peeks.

I suppose there is a possibility that if enough cooling holes are blocked that the engine performance (EGT vs FF) may actually improve as the air is deflected away from cooling back into the main stream and thus show up in trending. At any rate I'm sure that the engine trending experts are looking at their computer models specifically for advising operators who actually do this stuff on what to look for.

If anybody comes across some hard facts on this in todays climate please post.

[muduckace]

Very interesting article, I suspect that the cost of flight through volcanic ash may not be truely felt for some time to come, but it will come when engines start to fail power assurance checks and have to be replaced, it is not clear that anyone really knows what the cloud consists of and the effect of those contaminants on hot turbines, particularly the Willie Walshes of this world ! Keep your eyes on those gauges!

It was explained to me that ash can bond to, corrode and errode blades and other internals. All policy I understand is immediate possible engine change if flown into known ash.

[Self Loading Freight]

Well, we know that ash damages engines in subtle ways that can take a while to appear if you don't inspect immediately. The most recent thinking from the regulators looks to be that there are levels of contamination it's safe to fly through, levels that are risky and levels that are to be avoided at all costs... but as contamination is going to be cumulative, I don't quite follow that logic. Likewise, I'm not convinced by the "if you can't see it, it won't hurt you" thinking that some seem to have.; there have already been reports that the Mk 1 nose has detected conditions that the Mk 1 eyeball has not.

If we're going to be flying in any sort of ash cloud, I can't see an alternative to having quite sophisticated sensors that alert to conditions that require avoidance. They'll have to constantly check size, density and type of particulates, and relate that to a model of engine damage. That's not impossible: the sensor part may already exist, but probably not in a form suitable for widespread deployment.

Who's going do to this?

[muduckace]

Self Loading Freight

As a minimum internal inspection by use of boroscope equipment should be performed prior to next flight, even if clean I do not know if a dry/chem or wet engine wash would give the motor a clean bill of health. I would continue with the inspections at repetative intervals until the engine comes off wing.