WORLD METEOROLOGICAL ORGANIZATION =====================================

Transcription

1 WORLD METEOROLOGICAL ORGANIZATION ===================================== WORLD METEOROLOGICAL ORGANIZATION (WMO) IN CLOSE COLLABORATION WITH THE INTERNATIONAL CIVIL AVIATION ORGANIZATION (ICAO) AND THE CIVIL AVIATION AUTHORITY OF NEW ZEALAND FOURTH INTERNATIONAL WORKSHOP ON VOLCANIC ASH Rotorua, New Zealand, March 2007 Agenda Item 7: Volcanic Ash Warning Perspectives Title of Paper: The Gulfstream incident : Twin-engined flame-out over the Papua New Guinea highlands Authors: Andrew Tupper, Marianne Guffanti, Bill Rose, Herman Patia, Michael Richards, Simon Carn

2 The Gulfstream incident : Twin-engined flameout over the Papua New Guinea highlands Andrew Tupper 1, Marianne Guffanti 2, Bill Rose 3, Herman Patia 4, Michael Richards 5, Simon Carn 6 1 Bureau of Meteorology, Northern Territory Regional Office, Australia 2 U.S. Geological Survey, Reston, Virginia USA 3 Michigan Technological University, Houghton, Michigan USA 4 Rabaul Volcanological Observatory, Rabaul, Papua New Guinea 5 Cooperative Institute for Meteorological Satellite Studies, University of Wisconsin, Madison, Wisconsin, USA 6 Joint Centre for Earth Systems Technology, University of Maryland Baltimore, Maryland, USA ABSTRACT On 17 July 2006, a survey aircraft, a Gulfstream II, suffered a flame-out of both of its engines at high altitude over the mountainous and volcanically active country of Papua New Guinea. The crew were able to restart both engines at a lower altitude and land normally. Intensive investigations by all concerned have concluded that the engines most likely failed because a filter in both Fuel Flow Regulators had become blocked by volcanic ash. The most likely source for the ash is Manam volcano off the north coast of Papua New Guinea, which had been emitting copious amounts of ash at lower altitudes during that day. In order to attribute the source to Manam, we have to assume that a higher level emission was not observed from the ground observer s position on the mainland, and the ash and any other emissions were largely encased in ice aggregates at high altitudes and not observed by the crew. The lack of any other identified possible cause after investigation, the proximity of the volcano to the incident, the wind trajectories at the time, and possibly volcanic particles found in the filters together comprise a powerful set of circumstantial evidence. This incident appears to indicate a previously unknown threat to low-bypass type engines, and is the first flame-out incident to occur when the volcanic cloud has been too diffuse to be directly observed. INTRODUCTION During the development of the International Airways Volcano Watch, various incidents have been important in helping to characterise the extent of the threat to aircraft of airborne volcanic ash. The early incidents over Indonesia [Johnson and Casadevall, 1994] were relatively straightforward in the sense of being large, ashrich eruptions that caused extensive damage to engines and therefore presented an obvious threat. More recently two incidents in particular have helped us try to define the effect of very diffuse clouds: a) A NASA DC-8 encountered a 35 hour-old eruption cloud from Hekla, Iceland in February 2000 [Grindle and Burcham, 2002, 2003; Rose, et al., 2003]. The NASA DC-8 flew for seven minutes in cloud that had diffuse SO 2 and aerosols. The crew did not notice any performance issues in flight, but post-flight it was found that the aircraft engines sustained minor damage. b) On 23/24 November 2002, two aircraft flew through a diffuse cloud that was most probably from the explosive 3/5 November 2002 eruption of El Reventador, Ecuador, South America, approximately km east of the encounters [Tupper, et al., 2006]. Both crews noticed the cloud, but damage was only reported in the 23 Nov. case. This crew reported intense St Elmo s Fire, and light white smoke (ash) with burn smells (most probably indicating the presence of SO 2 together with the ash). The aircraft, an Airbus 340, had three Pitot probes replaced because of ash inside, some light abrasion on the engine air inlets but no damage on the windscreen or the nose. The encounter lasted about one minute at cruising speed, suggesting an area of distinct ash cloud of at least 15 km wide. In both the Hekla and Reventador cases, minor damage was recorded from old eruptions one an ash poor eruption (Hekla), and one an ash-rich

3 eruption but with a very old cloud. In neither case did the engines stop in flight. The case study described below gives a preliminary analysis of another intriguing incident, that may have far-reaching implications: an incident where a twin-engined jet aircraft apparently flew through cloud too diffuse to be noticed, but suffered a doubleengine flame-out at high altitude, and without sustaining engine damage. For this analysis we are indebted to the engine manufacturer, the aircraft operator, and the captain of the flight, who have given extensive information about the incident and their own investigations. DESCRIPTION OF THE INCIDENT On July , a Gulfstream II aircraft was engaged doing survey work over Papua New Guinea, flying at FL390 (~12 km amsl) near 6.2S 144.2E on a SW to NE mapping pattern, and relaying positions through a commercial passenger flight to their north on the Japan/Australia route. The Gulfstream was flying in apparently clear air. At 0518 UT (15:18 local time, or mid-afternoon), the righthand engine cut out, descent was initiated, and the other engine failed a minute later. The Captain of the Gulfstream asked the passenger flight to declare an emergency, and descended towards Port Moresby. At FL290 (~ 8.8 km amsl), the right-hand engine was successfully restarted, and the left-hand engine was regained at FL240 (7.3 km, approximately 3 km above the highest ground level in the area). The aircraft continued on reduced power to Port Moresby where it landed safely. The operators and engine manufacturer immediately launched an intensive investigation, which included boroscope engine analysis and fuel analysis. VOLCANOLOGICAL AND METEOROLOGICAL OBSERVATIONS There are a number of volcanoes of concern to aviation in Papua New Guinea, including Manam, Karkar, Langila, Ulawun, and Rabaul. On the day in question, volcanic activity was observed from Manam, which had caused considerable disruption to aviation during 2004/05, with months of eruption punctuated by paroxysms that produced ice-rich volcanic clouds to very high altitudes [Tupper, et al., 2007]. The eruptions had devastated Manam island and forced the removal of the population, including the volcanological observer, to the mainland. No instrumental monitoring was possible on that day, but from his observation post on the mainland, the observer reported that activity for that month peaked on the 17 th, with continuous emissions of thick, dark grey ash clouds to km above the summit (making the total emission height up to about FL100, or 3km). At the time of the incident (and therefore after any emissions that would have eventually led to the incident), the passenger aircraft doing position relays for the Gulfstream happened to be within visual range of Manam, and observed that a very dense, well defined ash cloud was projecting up to at least FL150 (4.5 km). It was difficult for the crew to tell the actual tops from their position as there appeared to be cloud cover at around that height as well. The apparent discrepancy between the heights from the ground and pilot observers is normal and could result from a number of causes. Another airline had also observed low level emissions from Manam that morning, although it was not reported until later. Satellite re-analysis from that day suggests a low level plume blowing to the west during that morning, which is further backed up by OMI SO 2 analysis, also taken during the morning. Around the time of the incident, the area was covered with cirrus cloud. Figure 1, from an image taken just over an hour before the encounter, gives a cloud height analysis for the area, using the application of CO 2 slicing outlined by Richards et al. [2006]. Between the image time and encounter time, the area of cirrus at altitudes greater than 12 km had drifted over the encounter location. Using the split-window (reverse absorption) method [Prata, 1989], and reflective techniques as previously used for Manam [Tupper et al., 2007], no evidence of high level ash was found nor was there any obvious evidence for an eruption cloud dissipating to the south found on OMI imagery the next day. Manual analysis of the hourly MTSAT-1R imagery suggests that the cirrus was moving southwards at about 50 knots (25 m/s), consistent with observations made from the Gulfstream of a northerly wind of 43 knots (22 m/s). Back-trajectories from the encounter location suggest that material would have come from the north, but have a much slower speed it is not unusual for model analysis in the region to be very poor due to a lack of timely upper-air observations. Taking 25 m/s as a rough speed, then the area of cirrus would have taken just under three hours to travel from the Manam region to the encounter location and would have been near the encounter location at the time of

4 the encounter. The cirrus itself appeared to originate from tropical thunderstorm activity to the north of the equator, but effectively obscured any volcanic activity at the time it passed over Manam. Neither the satellite analysis nor the ground observations suggest that there was a. paroxysmal-type explosion from Manam in our previous experiences, the large explosions will generally penetrate the cloud cover. However, it has been observed before at Manam that moderately strong activity can mix with the surrounding clouds but not be detectable from space [Tupper et al., 2007] Figure 1 Tropospheric cloud height analysis derived from 0405 UTC MODIS image using CO 2 slicing technique, just over an hour before the encounter. The approximate area of the encounter is circled in black, and the position of the volcano is labelled to the north. The arrow indicates the position of an area of cirrus-type cloud moving from near Manam towards the encounter location. Cloud altitudes are given in metres AMSL. WARNINGS CURRENT A NOTAM for ash to FL100 was current at the time with fairly general wording: CTN (Caution) due Manam volcano activity COOR (Coordinates) S / E Emitting smoke (sic) ash up to ft. The plume had not been noted during VAAC operations, and the pilot report of volcanic activity made during the incident did not reach the VAAC for some time, so there was no volcanic ash advisory current, and no SIGMET current, at the time of the encounter. Had they

5 been current, they would most likely have been issued to FL150 and so of little concern to the crew of the Gulfstream. OBSERVATIONS AND ANALYSIS FROM THE AIRCRAFT OPERATORS AND ENGINE MANUFACTURER No ash or sulphurous odours were observed by the aircraft crew. The engines were performing normally prior to the failure. External inspection of the engines showed nothing unusual. Extensive testing of the fuel was performed but the results were normal. Borescope inspection showed some very small amounts of a grey powder inside material examination by the manufacturer showed that the particles were mineral-based and principally composed of carbon, oxygen, calcium, sulphur and phosphor. The Fuel Flow Regulators (FFRs) were removed and subject to intense analysis. According to the manufacturer s reports, On different components of these assemblies fine mineral rich particles measuring from approximately 5 to 300 microns in size were found. The mineral based (sulphur, potassium, calcium, silicium) particles were sulphur rich. The manufacturer concluded after their analysis that a cylindrical filter in each FFR may have become blocked by volcanic ash, which at that altitude could have caused an engine flame out. On descent, the increasing pressure would have substantially cleared the filter, allowing an engine restart. On the basis of these analyses including the elimination of any other possible causes such as fuel contamination, the engine manufacturer believes that the double-flame out had been due to volcanic ash. The only test remaining is to take samples from Manam volcano and compare it to the samples collected from the engine parts. This will be done as soon as is possible. DISCUSSION AND CONCLUSIONS The event has several troubling aspects, chief of which is that nobody actually observed a volcanic cloud at FL390. In order to attribute this encounter to volcanic ash, we have to postulate that: a) any cloud from Manam at high altitudes was (as usual) ice-rich with ash particles ice-coated and non-abrasive, b) the cloud was diffuse enough to be classed as clear air, c) any free SO 2 contained within the cloud was below detectable levels, d) that the presumed emission to FL390 escaped the notice of the ground observer from his post at Bogia (possibly due to cloud), as well as the Darwin VAAC. However, we do know that the activity at the volcano peaked on that day, that the Gulfstream was flying backwards and forwards across the path of any high level emissions as it performed its mapping work, and that the engine manufacturer performed exhaustive tests to try to find another cause of the flame-out. Since the two engines flamed out almost simultaneously, it is unlikely that the failures were caused by prior ingestion of material. There is therefore little scope to reject the volcanic ash cloud hypothesis. The expert report of the engine manufacturer also leaves no doubt that, if we accept that the aircraft flew through volcanic ash, they have found a plausible mechanism for the double flame-out. How could this encounter and double flame-out have been prevented? Volcanoes such as Manam are so frequently active that it is not practical to close all nearby airspace without certain knowledge that ash is at high altitudes. A significant increase in the amount of available resources, such as the provision of weather radar and/or volcanic ash sensing cameras deployed to detect high altitude emissions, would be required to monitor each such volcano to the extent where we could be confident (even then, emissions lifted in cumulonimbus convection over the volcano would be undetectable). Cloud does and always will provide a strong inhibiting factor in remote sensing detection by the VAAC. While it is gratifying that the engines restarted properly and within design tolerances, we are unable to suggest that the International Airways Volcano Watch does not need to account for this kind of event. As a multiple-engine flame-out, the event qualifies as a Category 4 volcanic ash encounter [International Civil Aviation Organization, 2001], and the first to be associated with ash too diffuse to be observed by the crew. The failure mode hypothesised by the engine manufacturer is new and needs to be incorporated into education material, as well as into any relevant International Airways Volcano Watch

6 procedures. We emphasise that every single volcanic ash encounter, no matter how trivial, must be reported by aviation operators to help better define the threat. ACKNOWLEDGEMENT We are most grateful to the crew, aircraft operator and engine manufacturer for openly sharing their investigations with us. REFERENCES Grindle, T. J., and F. W. Burcham (2002), Even minor volcanic ash encounters can cause major damage to aircraft, ICAO journal, 57, 12-14, 29. Grindle, T. J., and F. W. Burcham (2003), Engine damage to a NASA DC-8-72 airplane from a high-altitude encounter with a diffuse volcanic ash cloud, Technical Memorandum, 22 pp, NASA, Edwards, California, USA. International Civil Aviation Organization (2001), Manual on volcanic ash, radioactive material and toxic chemical clouds., I I-2-7 pp, Montreal. Johnson, R. W., and T. J. Casadevall (1994), Aviation safety and volcanic ash clouds in the Indonesia-Australia region, paper presented at First International Symposium on volcanic ash and aviation safety, Seattle, Washington, U.S.A. Prata, A. J. (1989), Observations of volcanic ash clouds in the µm window using AVHRR/2 data, Int. J. Rem. Sens., 10, Richards, M. S., et al. (2006), Volcanic Ash Cloud Heights Using the MODIS CO2-Slicing Algorithm, paper presented at 12th Conference on Aviation, Range and Aerospace Meteorology, Atlanta, Georgia, 28 January - 2 February Rose, W. I., et al. (2003), The February-March 2000 eruption of Hekla, Iceland from a satellite perspective, in Volcanism and Earth's Atmosphere, edited by A.Robock and C.Oppenheimer, AGU Special Publication. Tupper, A., et al. (2006), Aircraft encounters with volcanic clouds over Micronesia, Oceania, 2002/03, Australian Meteorological Magazine, in press. Tupper, A., et al. (2007), Facing the challenges of the International Airways Volcano Watch: the 2004/05 eruptions of Manam, Papua New Guinea, Weath. forecasting, 22,