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AAIB Bulletin: 10/2011 G-YMMP EW/C2010/06/05

SERIOUS INCIDENT

Aircraft Type and Registration: Boeing 777-236, G-YMMP

No & Type of Engines: 2 Rolls-Royce RB211 Trent 895-17 turbofan engines

Year of Manufacture: 2001

Date & Time (UTC): 14 June 2010 at 1617 hrs

Location: Singapore International Airport

Type of Flight: Commercial Air Transport (Passenger)

Persons on Board: Crew - 12 Passengers - 202

Injuries: Crew - None Passengers - None

Nature of Damage: Extensive damage at rear of right engine nacelle and 

further airframe damage

Commander’s Licence: Airline Transport Pilot’s Licence

Commander’s Age: 44 years

Commander’s Flying Experience: 14,770 hours (of which 4,934 were on type)

Last 90 days - 192 hours

Last 28 days - 79 hours

Information Source: AAIB Field Investigation 

Synopsis

On departure from Singapore International Airport to 

London a number of EICAS (Engine Indicating and 

Crew Alerting System) messages were displayed for the 

right engine. During the climb the crew interrogated the 

system and established that the event had been transient 

and that it was safe to continue en route. During the 

flight there were further events associated with the 

right engine, showing increased fuel consumption and 

the crew elected to divert to Amsterdam, Netherlands, 

transmitting a PAN. After the aircraft landed safely it 

was found that the right aft inner nacelle was severely 

damaged and largely missing, with further minor airframe 

damage and this matched items of nacelle recovered 

from the runway at Singapore, but not yet identified. 

Examination indicated that the nacelle damage was 

due to thermal disbond originating from the HP3 duct 

area. There have been a number of separate but similar 

events in other airlines and the airframe manufacturer 

has issued a series of Service Bulletins to reduce the rate 

of occurrence.

History of the flight

The aircraft was on a scheduled flight from Singapore 

International Airport to London Heathrow Airport. Due 

to the length of the sector four flight crew operated the 

flight: a commander and co-pilot, and a ‘heavy’ captain 

and co-pilot. The commander was the handling pilot for 

the takeoff and climb to cruise.
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The commander and both co-pilots were on the flight 

deck for the start up, takeoff and climb to cruising 

altitude. The start up was uneventful, however due 

to a high takeoff weight, with a minimal derate to the 

engines’ thrust, high EGTs were expected during the 

takeoff and briefed by the commander. At this time it 

was dark.

The aircraft took off from Runway 02L at 1617 hrs on 

14 June 2010. At approx 500 ft aal the right engine’s 

EGT fluctuated by approximately ± 100°C and the ENG 

THRUST R caution message momentarily illuminated 

on the Engine Indication and Crew Alerting System 

(EICAS), along with the ENG RPM LIMITED R advisory 

message. At this point the flight crew also noted that 

the right engine’s N1 was at its maximum of 100.5%. 

As no recall items were required from the QRH the 

autopilot was engaged and the departure continued 

while the situation was monitored. At acceleration 

altitude the thrust was reduced to ‘climb thrust’ on both 

engines; the ENG RPM LIMITED R message cleared and 

both engines’ parameters settled in their normal range.

At a suitable point in the climb the STATUS page and 

Maintenance Access Terminal (MAT) were accessed by 

the co-pilots; an EEC C1 R status message remained but 

this required no crew action. The MAT showed several 

discrete failures, including a ‘short’ on the fire loop for 

the right engine core. Interrogation of the maintenance 

pages produced an automatic snapshot of the engine 

event after takeoff. This showed that the right engine’s 

N1 had reached its limit, with fuel flow, EPR, EGT, N2 

and N3 all depressed during the event.

With both engines apparently running normally, as 

the aircraft climbed through 10,000 ft the commander 

disconnected the autothrottle and selected full thrust as 

a ‘confidence and troubleshooting’ check. Full rated 

thrust was achieved, although N1 was higher on the 

right engine. Climb thrust was re-selected and the 

autothrottle re-engaged. The crew elected to continue 

en route while evaluating the situation. Possible causes 

were considered to be a birdstrike, fan damage, spurious 

indications or a failure within the EEC or associated 

systems. At this stage the only unusual indication was 

that the right engine N1 was approximately 3.5% higher 

than the left engine. At this point the ‘heavy’ co-pilot 

went into the cabin for his rest.

Once the aircraft had reached its initial cruising altitude 

the only technical discrepancy was that for a given 

EPR, the right engine’s N2, N3, fuel flow and EGT 

were depressed compared with the left, while the N1 

was higher. The crew considered possible fan damage, 

but the vibration indicator showed only 0.8 units1, with 

N2 being the dominant item. Maintenance control 

in London was contacted to discuss the possibility 

of erroneous N1 indications, as this seemed a likely 

cause of the displayed symptoms; they suggested it 

was unlikely. A higher noise level reported from the 

cabin was also discussed, and the likely cause of this 

was deemed to be an ongoing issue with the wing root 

fairing, which had been recently subject to a tape repair 

due to previous reports of cabin noise.

Approximately 4 hours into the flight an ENG EEC MODE 

R advisory message was displayed on the EICAS and 

the QRH checklist actioned. The EEC has two control 

modes, ‘Normal’ and ’Alternate’ and this message was 

advising that the right engine had switched to ‘Alternate’ 

Footnote

1 The engine vibration monitoring system is primarily intended for 

engine condition monitoring, but it is also a useful tool for isolating 

and determining corrective action for engine anomalies. There is no 

certified vibration limit, but when a high vibration level is reached, 

the secondary engine parameters are automatically displayed. Since 

there are no operating limitations for the airborne vibration monitoring 

system, there are no specific flight crew actions (or procedures) based 

solely on vibration indication.
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mode; as part of the QRH actions, the crew also switched 

the left engine to ‘Alternate’ mode . Given the MAT 

indication of several failures in this area and the EEC C1 

R status message this was not a cause for alarm for the 

crew as they had suspected EEC issues. Following this 

action, the discrepancy between left and right N2, N3, 

and fuel flow increased, as would be the case if the right 

N1 was over-reading; vibration remained normal.

The crew consulted the “Performance In Flight” section 

of the FCOM 1 relating to Alternate Mode EEC. This 

suggested a 20 tonne decrement to ‘primary mode’ 

performance limit weight for climb and net level-off 

weight. The crew decided that climb decisions would 

be based on this higher assumed weight.

Approximately 5 hours into flight the Flight 

Management System’s ‘fuel remaining’ calculations at 

London Heathrow started reducing. While the required 

thrust and fuel flow were high they were not entirely 

inconsistent with a 20 tonne performance decrement, 

although the fuel flow was higher than would be 

expected. As a result, reaching London Heathrow with 

the minimum required fuel of 5,400 kg was becoming 

unlikely, and the trend was worsening. At this point 

the aircraft was over Afghanistan and the route ahead 

had few suitable alternates for several hours. The crew 

considered that if a turnback were attempted it would 

still be several hours before the aircraft would reach an 

acceptable alternate airport. As the fuel on board was 

about 52,000 kg of fuel and total fuel flow was about 

8,000 kg/hr the crew felt it was prudent to continue 

towards better alternates, with several less suitable, but 

usable, places to go if conditions worsened. A crew 

handover took place and it was agreed the ‘heavy’ 

crew would continue to monitor the situation closely, 

liaise with operations, and advise the operating crew if 

conditions deteriorated.

Approximately 8 hours 45 mins into the flight the 

commander was woken in his rest bunk by what he 

believed was an engine compressor stall. As the engines 

continued running, with no change in thrust, he decided 

it had been imagined. The relief crew heard a “thud” 

and felt a slight movement of the aircraft. They then 

noticed that the required thrust setting and fuel flow had 

reduced, and that the fuel state, although now showing 

insufficient for London, had stopped deteriorating. 

They then began planning what options were available, 

given the remaining fuel state, and contacted the 

operator to see which alternates were preferable. The 

‘heavy’ crew suspected that a panel had become loose, 

creating drag for several hours, and suddenly detached. 

As it was now daytime the ‘heavy’ captain examined 

the aircraft exterior as far as possible but could find 

no evidence of missing panels or other damage. The 

rear of the engine was not visible from the cabin. 

The possibility of reverser blocker or cascade doors 

detaching was considered, although engine parameters 

remained unchanged. 

The crew elected to divert to Amsterdam International 

Airport, Netherlands, primarily because the weather 

was excellent, multiple runways were available and 

the aircraft would arrive with about 2,000 kg above 

minimum reserve fuel, thus allowing for contingencies. 

Having established that rated thrust was available 

from the right engine, a standard Flap 25 landing was 

planned. As the crew did not know how many track 

miles remained or which runway to expect prior to 

establishing contact with Amsterdam ATC, and any 

delay caused by ATC or a latent technical problem 

might have resulted in landing below reserve fuel, they 

transmitted a PAN on initial contact. The aircraft landed 

without further incident, using idle thrust reverse, at 

0511 hrs on 15 June 2010. Having vacated the runway 

near the AFRS, who were on standby, the commander 
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elected to get visual inspection from them; this was 

inconclusive.

After shutdown and passenger disembarkation the 

crew vacated the aircraft to see if there were signs of 

damage. They discovered that the aft inner nacelle on 

the right engine was severely damaged, and much of it 

missing, and that there was further airframe damage.

Engine debris at Singapore International Airport

Aircraft parts were found by a Singapore International 

Airport Airside Operations vehicle on the edge of 

Runway 02L during a scheduled maintenance closure 

of Runway 01 on 14 June at 1715 hrs (0115 hrs 

Singapore time). Attempts were made to identify the 

parts, but without success. At 0843 hrs (1643 hours 

Singapore time) on 15 June 2010 the airport authorities 

received a call from the operator of G-YMMP, saying 

that parts of an engine nacelle were missing on 

arrival in Amsterdam. The operator’s representative 

in Singapore subsequently identified the parts as 

belonging to G-YMMP.

Initial examination

The operator and the airframe manufacturer made 

initial assessments at Amsterdam of the damage to the 

aircraft. It was clear that the left inner wall ‘D-duct’ on 

the right engine thrust reverser had separated from its 

engine and that a large portion of the turbine exhaust 

nozzle was missing (Figure 1). There was also damage 

to the inboard flap fairing and flaperon, consistent 

with the separation of the items from the engine, with 

scraping and gouge damage on the right lower wing 

skin and the right horizontal stabiliser.

The manufacturer’s initial examination indicated that 

buckling damage to the inner wall D-duct was consistent 

with a: 

‘typical of loss of stability due to disbond of inner 

facesheet’

and that this form of failure had been seen on a 

number of previous occasions. It appeared likely that 

Figure 1

Thrust reverser buckled inner wall and missing nozzle
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AAIB Bulletin: 10/2011 G-YMMP EW/C2010/06/05

the separation of the turbine exhaust nozzle had been 

caused by the failure of the duct structure as the inward 

collapse of the inner wall applied bending loads to the 

nozzle supporting structure.

This initial examination by the manufacturer also 

indicated areas in which there did not appear to be 

sufficient sealant to preserve firewalls, such as on the 

leading edges of the insulation blankets, around cooling 

tube penetrations and around the interface between 

the left HP3 duct and the insulation blankets, without 

evidence as to how much this had contributed to the 

failures. The airframe manufacturer reported that: 

‘preliminary results of hardware and engine fault 

codes and QAR data are consistent with the loss 

of the nozzle being secondary to the loss of the 

inner wall.’

Thrust reverser thermal barrier system - description

The affected parts of the thrust reverser system and 

engine cowlings are within the design responsibility of 

the airframe manufacturer, not the engine manufacturer. 

The maintenance manual for the aircraft describes the 

function of the thermal barrier protection applied to the 

thrust reverser as being to keep it:

‘structurally serviceable’

and to prevent: 

‘parts separating from the airplane in flight.’

The inner wall of the fan duct cowl (Figures 2 and 3) is 

a composite material susceptible to; 

‘radiant heat damage from fires and [normal] 

engine operation’ 

Figure 3

Location of thermal blanket seals in fan duct cowl

(courtesy Boeing)

Figure 2

Thrust reverser thermal barrier in fan duct cowl

(courtesy Boeing)
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without the thermal barrier. The barrier consists of 

thermal insulation blankets installed in the area bounded 

by the fire seals in Figure 3. 

The integrity of the blanket-to-blanket seal, the blanket 

penetration seals and the blanket edge seals is critical 

to the success of the thermal barrier protection and to 

the preservation of the structural integrity of the thrust 

reverser inner wall. The maintenance manual states that 

large amounts of hot (leaked) compressor air: 

‘can penetrate through the gaps between the 

overlapped blankets to cause convective heat 

damage to the T/R inner wall’ 

and that it is: 

‘important to find any holes in the bleed offtake 

pneumatic ducts, or gaps at pneumatic duct 

connections, or damaged kiss seals and kiss 

seal mating surfaces during engine visual 

inspections.’

Flight data recorders

Data downloaded from the flight data recorder (FDR) 

for the incident flight is presented in Figures 4 & 5. 

Figure 4 shows the takeoff and climb to 7,000 ft amsl 

from Singapore International Airport. At 1618:35 hrs, 

as the aircraft climbed through 500 ft, the right engine 

Figure 4

FDR data for the takeoff, showing right engine fluctuations
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Figure 5

Salient FDR parameters of incident flight
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N1 increased from a nominal 99% to 100.5% and the 

left engine remained at 99%. At the same time, the 

right engine EGT dropped from 867oC to 448oC and 

then fluctuated around 700oC for about 130 seconds, 

before rising to 750oC; the left engine EGT remained 

steady at 865oC, dropping smoothly to 750oC as the 

engine thrust was reduced to climb thrust.

Figure 5 shows data for the complete flight to London 

Heathrow Airport. Also indicated on Figure 5 are 

the EICAS messages displayed to the crew. These 

messages were recorded on the Maintenance Message 

Data Report, downloaded from the EICAS after the 

flight. The first set of messages were at 1618 hrs during 

the time of the right engine EGT fluctuations. However, 

the report only records the time for each message as 

hours and minutes so the exact timing is unknown. For 

the next four hours the EPRs and fuel flow for both 

engines were matched but small discrepancies between 

the engines were recorded for N1 (1 to 3.5%RPM), N2 

(0 to 1%RPM), N3 (1 to 2%RPM), and EGT (0 oC to 

8oC).

The second set of EICAS messages occurred at 2023 hrs, 

approximately four hours into the flight, as the right 

engine EPR signal was lost. It was at this point the 

engines switched from Normal EEC mode (‘EPR’) to 

Alternate EEC mode (‘N1’). From this point onwards 

the engine N1s were matched but discrepancies 

between the engines (left greater than right) were 

recorded for fuel flow, N2, N3 and EGT. In particular, 

a 5% difference in fuel flow was measured, increasing 

in steps to 15% by the end of the cruise portion of the 

flight. Also recorded was a lateral asymmetry to the 

right: rudder trim (not shown) was only used between 

0254 and 0320 hrs, when 0.05 inches of left rudder trim 

actuator movement was recorded.

Engine performance review

During the investigation, the engine manufacturer 

conducted an analysis of the performance of both 

engines during the flight, primarily using data from 

the EHM (engine health monitoring) and QAR (quick 

access recorder).

This analysis reflected the account of the flight given 

by the flight crew and by the FDR data. In particular, 

it identified the anomalies between N1 and EPR during 

the initial event at takeoff and the relatively high power 

settings on both engines during the first four hours of 

flight, reflecting, and compensating for, some degree of 

exhaust nozzle area change on the right engine. 

Following the event at about four hours, and the 

switching to ‘Alternate’ EEC mode (controlled by N1, 

rather than EPR), the higher power settings continued, 

with the left engine reflecting scheduled performance but 

the right engine performance degraded by the changes 

in effective nozzle areas. The total fuel consumption 

by the engines, resulting in the PAN diversion into 

Amsterdam, matched the aircraft tank quantities. 

Detailed examination

Following the initial investigations at Amsterdam and in 

the United Kingdom, the significant items from the failed 

duct on G-YMMP were despatched to the USA for more 

detailed investigation at the airframe manufacturer. 

During this examination the manufacturer identified 

several locations with clear indications of thermal 

exposure and disbond. Of those, the location of greatest 

interest was around the drag link fitting, immediately 

above the HP3 cutout (Figure 6). This was among the 

more discoloured areas, and it was clearly included in 

the disbonded region of the panel. The discolouration of 
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other areas of the inner wall was evidence of overheating 

at those locations, but the manufacturer reported that 

discolourations outside the disbond region associated 

with the panel collapse were ‘unlikely to be implicated 

in the failure’of the panel. This was consistent with the 

manufacturer’s initial assessment at Amsterdam.

The manufacturer further noted significant 

characteristics of the disbonded surface. These 

included areas with low bond strength, as evidenced 

by small fillet scars and/or adhesive failure between 

the honeycomb core and the facesheet, and a region 

of significantly overheated adhesive between the drag 

links next to the HP3 cutout.

Service history and safety actions

This was the first event of this type experienced by the 

operator of G-YMMP but it followed approximately 

10 other events on 777 aircraft with this airframe-engine 

combination. A further two events have been recorded 

since that to G-YMMP.

As a result of the initial incidents, in February 2005 

the aircraft manufacturer issued Service Bulletins 

777-78A0059 and 777-78-0060. These SBs principally 

involved one-time inspections of the thrust reverser 

inner wall, insulation blankets, compression pads, and 

drag link fittings (-059), and the application of sealants 

(-060).

Following further events at other operators, one of 

which was on an airframe which had SBs -059 and 

-060 correctly completed, an additional Service 

Bulletin, 777A78-0065 was issued in June 2008, 

requiring recurring inspections. Initial inspection of 

the blanket sealing on G-YMMP was carried out on 

5 February 2010 and a repeat inspection was carried out 

on 14 May 2010, with no significant damage reported. 

However, a full NDT inspection of the inner wall with 

all the thermal blankets removed had not yet been 

completed on G-YMMP at the time of this incident, as 

the inspection was not yet due.

The airframe manufacturer issued a further, and 

extensive, Service Bulletin in late 2009, 777-78-0071, 

stating that the existing thermal protection system 

was insufficient to prevent damage to the inner 

wall of the thrust reverser and incorporating a new 

thermal protection system to reduce the temperatures 

experienced by the inner wall during flight. There was 

some initial delay in the approval by the EASA of the 

design change included within this Service Bulletin, 

as EASA was requesting further data and design 

substantiation from the airframe manufacturer, and the 

design change had not been fully approved at the time 

Figure 6

HP3 duct disbond location
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of this event to G-YMMP (14 June 2011). However, 

the operator of G-YMMP commented that, even with 

earlier EASA approval, the scope of the work and the 

number of aircraft to be covered leaves it uncertain 

whether G-YMMP would have been modified by the 

date of this incident.