Ground procedures for ash detection

[brooksjg]

I'm neither ground engineer nor (in fact) pilot but I've been watching the discussions about volcanic ash over on the flight deck forum with some interest.

Now we have some wriggle room for flying in the presence of ash, it's often going to be up to you guys to call the shots. If you study the reports (especially the one about the 1992 incident involving a DC-8 - ref http://www.nasa.gov/centers/dryden/p...ain_H-2511.pdf) you'll see a major problem which will now be heading straight towards YOU. Did an aircraft REALLY encounter ash and if so how much? In the 1992 DC-8 case, the flight deck crew KNEW that there had been an encounter but despite this could find no evidence despite thorough checks in Kiruna. As a result, the DC-8 flew another 70-odd hours without incident and it was only when it got back to Edwards AFB in the US that serious engine damage (repair bill $$m) was discovered. European commercial aviation is now in a similar situation but with THOUSANDS of aircraft and ash encounters. In most cases, there will be NO obvious damage and / or distress symptoms from the turbine instrumentation. Nevertheless, turbines, in particular, may have sustained serious damage internally.

It occurs to me that you are ALREADY changing filters on engines as part of routine maintenance. At least the filters on the cabin pressurisation system air feeds will DEFINITELY contain a sample of whatever the aircraft has flown through since the last change. Problem with thes particular ones is that the air volume can be adjusted. I'm not a systems expert - it may be that there are OTHER air filters that handle a fixed percentage of the total air passing through the engine and would therefore give a more accurate indication of how much inlet air contamination had occurred since the last filter change - the NASA report mentions specifically heat-exchanger filters.

Questions: how often do these filter (sets) get changed? Is any analysis already done to check the extent and character of contamination in them?

Seems to me that in the extreme case where it is ESSENTIAL to know whether an ash encounter has occurred, a check AFTER EVERY FLIGHT might be necessary.

Another question: for the most suitable and accessible filter, how long would it take, on the apron, to change it?

You can probably already see where I'm going with this! There are probably serious Brownie Points for an Ash Detection System that couldbe applied to any aircraft with vulnerable turbines.....

[Blacksheep]

We (the airlines) have already implemented specific additional maintenance inspections for ash detection and monitoring, including the necessary maintenance actions if those additional inspections turn up any evidence of ash contamination. In fact, the volcanic ash maintenance practices have been in the applicable manuals for many years. All the major airframe and engine manufacturers have included volcanic ash procedures in their recommended maintenance procedures since around 1990. Similar comment can be applied to flight operations and the operating recommendations.

The problem in the European debacle was a failure by the authorities to identify the actual ash concentrations and circulate that information to those concerned with maintaining the aircraft. The easy "knee jerk" response, citing "Safety is Paramount" as some sort of religious mantra was employed without due regard to the inevitable consequences of a long term shut-down of air transport. The industry as a whole is perfectly capable of handling ash encounters as long as the relevant specialists are properly informed of the actual conditions. Heads should roll, but they probably won't.

Very dramatic incidents, such as the BA009 four engine failure, were the result of aircraft inadvertently flying directly into the main cloud. The true concern over Europe was the longer term effects on aircraft flying in the dispersed plume, where, even though ash was present, it was in much smaller concentrations than that needed to cause immediate catastrophic effects - more of an economic concern than a safety matter.

[brooksjg]

Thanks for your (general) answer.

My questions were quite specific, mostly because it seemed to me on available evidence (in the case of the airlines, actually very little!) that the existing volcanic ash diagnostics were probably not quick and possibly not effective. Note that ALL the reportage and also operational pilots' comments I've seen on the technical aspects of ash investigation have focused on only two things: external, physical checks and borescoping. The first seems to be ineffective with respect to ash (see NASA report I referenced) and the second is certainly not going to be quick!

I'm entirely with you are on the key difference between catastrophic IFSDs as a result of flying through dense ash and the much more costly (!!) long-term impact via increased costs for post-flight checks AND turbine maintenance on the far greater number of aircraft affected by much lower ash densities.

If it turns out that the other parties (Met Office, ...?) CANNOT provide sufficiently detailed volcanic ash forecasts including both location AND particle characteristics AND ppm in the intake air, as seems to be the case right now, it's down to you guys to run the best diagnostics and then do the required maintenance on the correct aircraft.

First-line investigation using long-winded methods (borescoping?) on the apron is not a realistic option. That was my motivation for asking about filter analysis - simple questions for which I hoped there'd be simple answers.

[Bus429]

FODCOM 12/2010

[spannersatcx]

First-line investigation using long-winded methods (borescoping?) on the apron is not a realistic option.

We did one yesterday!

We have extra checks to do each transit, if nothing reported by the crew, using MK1 eyeball, if you find anything then there is a conditional inspection in the MM Chpt 5, that will take a while, lots more things to check and replace.

[brooksjg]

FODCOM 12/2010

Yes well.....

One main reference to ground maintenance procedures with no actual guidance at all, plus a few oblique references. Main emphasis as far as detection goes placed on flight crew. Baloney! As was reported by NASA, you can fly a DC-8 through thick ash that does $2m+ worth of damage and make no useful observations at all, of instruments or out the window! And then the crew (not, I think, ground engineers) do a Mk1 Eyeball check after safely landing, and STILL find nothing. And these guys KNEW there had been an ash encounter because extra (scientific) instrumentation on board had detected SO2. Do you think that given these (well-known?) facts, the Mk1 eyeball is enough as Step 1, given that you say additional checks depend on Step 1 finding something?

To quote from the NASA DC-8 Incident Report:

There are currently no fully reliable methods available to flight crews to detect the presence of a diffuse, yet potentially damaging volcanic ash cloud.

I know of no changes from that position since 2003.

[Paully617]

ash clearance

hi spanneratcx, where do you work then??

[TURIN]

hi spanneratcx, where do you work then??

Don't tell 'im Pike!

I saw you all beavering away. The security bloke was telling all and sundry you had found ash in the no.3 engine.

Did the 'scope reveal anything interesting?

[spannersatcx]

Don't know what you mean!

We found something, not sure it was ash, more like sand, but the inspection is the same for ash or sand, BSI, drop filters change oil etc. Got some pics of the inside most of it was pretty clean except......

[Blacksheep]

Questions: how often do these filter (sets) get changed? Is any analysis already done to check the extent and character of contamination in them?

The various filters are checked as part of the standard Approved Maintenance Programme. The volcanic ash precautions use escalated intervals that depend upon aircraft types so it isn't possible to be specific, but in general a filter change that is normally scheduled at C interval may, for example, be escalated to an A interval. And yes, the intervals are set based upon existing analysis - i.e. condition monitored maintenance. All commercial airplane maintenance programmes are supported by continuous monitoring through system and component reliability monitoring and analysis.

Incidentally, the turbine blades and inlet guide vane images in that NASA report are meaningless without comparison images of the allowable condition of a blade. Blades that are classed as serviceable might in some cases look in much worse condition than those illustrated.

[brooksjg]

The various filters are checked as part of the standard Approved Maintenance Programme.

Yes - obviously.
But what about analysis of whatever has been caught in them? And what triggers escalation of the change from C to A?

The whole point I was trying to get over is that filters on bleeds from the compressor stage of the turbines seem to be currently the ONLY 100% reliable indicator of what the aircraft has flown through since the last filter change and therefore the ONLY method immediately available to determine what other examinations are needed.

If it currently takes some OTHER indication (visible ash somewhere on the aircraft, flight crew reports, ...) to cause a filter to be changed 'early', that's looking at the whole issue the wrong way round.

The pictures of the blades are pretty-much irrelevant - you may well be correct that what is actually visible is 'acceptable wear and tear'. However, if a GE overhaul facility says that one of the disks could have had a blade failure 'within 100 hours' and NASA decided to part with $3.2m for an engine overhaul, there must have been a lot of damage (or NASA is VERY gullible!). The key information is not until page 13.

I'm looking at this whole issue from the point-of-view of the front line. If something nasty (or maybe just expensive) happens in spite of extra inspection as per the FOD, I suppose the blame passes to CAA but I'd also point out that the FOD itself includes everything bar the kitchen sink! VERY hard to PROVE that everything in it was done.

[Blacksheep]

And what triggers escalation of the change from C to A?

A report from the applicable Meteorological Service that a volcanic eruption has occured in the vicinity of flight paths operated or proposed to be operated by the aircraft in question.

SOP is:
Volcano erupts
Met Service reports extent and density of the ash plume
Authorities publish "No Fly" notices for specific high density locations
Airlines re-route to avoid the plume
Airlines implement precautionary measures for flight in areas where lower concentrations of ash may be encountered

Infra-red satellite monitoring of the globe is taking place at roughly 15 minute intervals across the globe and the findings circulated. The failure of the European authorities to adhere to the established methodology resulted in the European "No-Fly" zone being held in operation far beyond the necessary period and led to the subsequent open defiance demonstrated by large, capable and influential European carriers like LH, KLM and BA.

Internationally, such carriers will regularly operate in other volcanic zones. There are, after all as many as 24 volcanoes in various stages of eruption at any time around the globe. A volcanic eruption affecting Europe may be big news but it is an almost routine event around the world.

...could have had a blade failure 'within 100 hours' and NASA decided to part with $3.2m for an engine overhaul, there must have been a lot of damage

No, the report says that on the engine that had the most damage, "hot section parts may have begun to fail if operated for another 100 hours". The report indicates that this engine had flown 388 hours since the last shop visit but does not say what that shop visit was. Total engine hours on each engine were stated as in excess of 5,000 hours, but it is engine cycles that are the more important tracking value for engine maintenance. One would suspect that a NASA research aeroplane would have fewer hours per cycle than an in-service long-haul airliner routinely operating seven to eight hour sectors, would be less likely to use de-rated take-off and climb settings and, with 17 experiment stations would operate at higher all-up weights.

The report also includes evidence of a previous sand ingestion event that was serious enough to warrant a boroscope inspection. Though there were no significant findings, this event must have some bearing on the final condition of the rotating parts. i.e. the total damage was not confined to the ash ingestion.

The repair bill was for all four engines and $3.2 million for one engine overhaul and three engine refurbishments would not be considered unusual.

I guess I'm saying that this one event to an atmospheric research aircraft that seems to have been deliberately flown close to a volcanic plume, leaves as many questions unanswered as it answers and is therefore not a good example to quote with reference to commercial operations in a potential volcanic ash ingestion environment.

I'm personally acquainted with a fleet of B757s that operated in the South China Sea area during and since the Pinatubo eruption that closed Clark Air Force Base permanently due to ash fallout. Local conditions in the rest of SE Asia were similar to those that pertained in Europe recently, yet those engines suffered no adverse symptoms, achieved a normal service life with unimpaired reliability and during their routine shop visits, showed no signs of unusual damage. In fact, although the airframes have long been scrapped, those engines remain in service on other aircraft.

[brooksjg]

Thanks for the much more-definite information from the Real World!

To avoid confusion about quotation from the NASA report, I was quoting from the summary. The relevant part reads

There was no evidence of engine damage in the engine trending results, but some of the turbine blades had been operating partially uncooled and may have had a remaining lifetime of as little as 100 hr

OK -not much different but it SOUNDS more serious. In the same section, there's another interesting sentence:

There are currently no fully reliable methods available to flight
crews to detect the presence of a diffuse, yet potentially damaging volcanic ash cloud.

Elsewhere, it also states that material found in the cabin A/C pack heat exchangers was ash, not sand. I'm afraid that taking this and other statements together, I discounted the previous sand ingestion, probably wrongly.

The only other outstanding questions:
Precision and timeliness of direct observation of the plume(s). If it is indeed the case that satellite observations are possible as frequently as every 15 minutes and that from these sufficient data about the number of (potentially overlapping) plume layers, their density in particles/cu metre and their height can be obtained, then you're quite right. What's all the European fuss about? However, my impression was that satellite data was not that timely or precise, other observations were patchy and plume modelling by computer was not accurate enough for an adequate risk analysis for a given route. I stand corrected.

Cumulative effects. If unreported ash encounters can and will take place, what backstop currently exists in post-flight checks and maintenance to identify cumulative damage due to ash ingestion?

Ps For a Horses Mouth audio report on the NASA incident, see Volcanic Ash Cloud Encounter.
One important point that emerges is that if ash particles in the plume get covered with ice, the satellite imagery cannot distinguish between ash and normal cloud. What's not made clear is whether the preceding VAAC ash report positions were wrong because of incorrect modelling or because the satellite imagery took precedence but was misleading.