1. The document summarizes a project to inspect GE90 engines on Boeing 777 aircraft operated by Emirates due to issues with the stage 1 high pressure turbine shrouds. The author planned and oversaw inspections and engine removals to implement a permanent modification. 2. As maintenance planning officer, the author's role was to minimize operational impacts through precise planning of the monthly inspection schedule and engine removals in coordination with other departments. Technical knowledge of the engines and inspection process was required. 3. Through careful analysis of inspection findings and coordination between teams, the author was able to identify deterioration trends and schedule engine removals to implement modifications before any incidents occurred, closing the inspection requirement.

1. 1
Work Project 2
Planned and executeda major inspection on all Boeing 777 (operatedby
Emirates)GE90-110B/115B Engine-HighPressure Turbine Stage 1 Stator
Shroud On-Wing Boroscope;Supervised the engine removals for carrying out
permanent modification
2.1 Introduction
This project was undertaken during my tenure with Emirates Airlines, Dubai (UAE) between
June 2010 and November 2011 while I was working in the Aircraft Maintenance Division as
Planning Officer. Emirates is the largest fleet operator of Boeing 777 and Airbus 380 in the
world. The core value of Maintenance Planning revolves around the key driving factor of
ensuring an airworthy and safe fleet without affecting the operational requirements of the airline.
2.2 Background
Boeing 777 aircraft is broadly classified into two categories – Classic Fleet which consists of
Boeing777-200/300/200ER and New Generation Fleet which consists of 300ER/200LR.
Classic Fleet can be powered by three options of engine manufactures in the market.
 GE90-94B engines are made by General Electric
 Trent800 engines are made by Rolls Royce
 PW4000 engines are made by Pratt & Whitney, while
New Generation Fleet can be powered only by GE90-115B and GE90-110B for Boeing777-
300ER and Boeing777-200LR respectively.
Emirates had a fleet size of ninety eight Boeing 777 aircraft at that time.
The different variants of the aircraft which Emirates had were,
Boeing777-200, 3 in total fitted with Trent 800 engines
Boeing777-300, 12 in total fitted with Trent 800 engines
Boeing777-200ER, 6 in total fitted with Trent 800 engines
Boing777-300ER, 67 in total fitted with GE90-115B engines
Boeing777-200LR, 10 in total fitted with GE90-110B engines.
Since this project was based on the inspection requirements of stage 1 HPT shroud, it is
necessary to understand the details of the cause, investigation, inspection process and the
terminating action for this critical inspection.
2.3 Technical understanding of actual incident
The project was a result of the following incident and the consequent developments: -
One of the airline operators was operating Boeing777-300ER fitted with GE90-115B engines.
Just after take-off during the initial climb-out, at approximately 2160 feet above sea level, the
number 2 engine lost power. Despite the fact that all engine parameters showed normal readings

2. 2
while the aircraft commenced its take-off from runway, Engine Indicating and Crew Alerting
System (EICAS) parameters displayed rapid decreases in fan speed (N1), compressor speed
(N2), fuel flow, and oil pressure after take-off. The exhaust gas temperature (EGT) increased and
peaked at 1252ºC within 2 seconds of the engine failure with EGT exceedance indication in the
flight deck. This was accompanied by a rise in engine vibration levels as well. Fuel to the engine
was cut off by the crew and the aircraft was stabilized with one working engine. Then it was
safely landed after declaring emergency and was towed to the hangar for examination.
2.3.1 Technical understanding of Power plant
Detailed understanding of the turbines, compressors is an absolute requirement for a successful
planning and the execution of the inspection.
GE90-115B/110B Engine primarily consists of the following components.
 9 stages of High Pressure Compressors (HPC) driven by 2 stages of High Pressure
Turbines (HPT)
 4 stages of Low Pressure Compressors (LPC) driven by 6 stages of Low Pressure
Turbines (LPT)
 Dual dome annular combustor
Preliminary inspections revealed small fragments of high-pressure turbine (HPT) and low-
pressure turbine (LPT) hardware in the engine exhaust cone. This damage was consistent with
excessive heat and impact from debris originating from forward of the LPT stage but there was
no damage to the engine cowlings observed. However, there was heat damage to
the HPT module near the HPT active clearance control panels.
Further inspection of the propulsor using boroscope revealed extensive damage to HPT Stator
Shroud as well. The disassembly of that engine revealed that the initial distress was located at
the HPT shroud position number 33.
2.3.2 Identifying the root cause
Damage leading to liberation of any hardware has a cascading effect which only causes further
damage to the parts downstream of the direction of airflow. To locate the origin of damage, the
procedure adopted involves an inspection beginning from the furthest point downstream on the
engine which is the exhaust and working back through the LPT and HPT stages by observing the
progress of damage up to a point upstream where there is no damage found.
In this scenario, there was no damage observed to the forward of stage 1 HPT stator and rotor
indicating the origin of the damage.
It was also determined that the damage was caused due to severe heat distress in that area since
the affected area showed excessive burn marks and missing shrouds.

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2.3.4 Inference of the Investigation:
Under the right operating conditions, a fuel-rich zone at the combustor can exist downstream
towards the turbine section. In normal conditions, this fuel-rich zone would pass through
the HPT and into cooler temperatures following work extraction in the turbine stages with no
effect on engine operation.
HPT stator shrouds have cooling holes which have bleed air entering through the holes tapped
from cooler sections of the engine to dissipate the extreme heat coming into the HPT section of
the propulsor.
However, if a hole greater than 0.3 inches in diameter exists in HPT stage 1 shroud, the hot fuel-
rich air can be ingested in the region behind the shroud against the force of cool air flowing in
through the hole. The larger volume of cool air rich in oxygen in this region can mix with the
fuel-rich air and become a super-heated zone. The temperatures of this super-heated air mixture
would be well above the melting point of the surrounding materials, which would quickly lead to
rapid deterioration of the shroud hanger and stage 2 nozzle outer bands. This would lead to the
liberation/ release of a stage 2 nozzle and cause the resultant downstream hardware damage.
GE suspected that shroud failures were attributed to the machining process used to drill the
cooling holes in the shrouds. The holes were laser-drilled into the shrouds, and during
production, a higher-intensity lamp was used to drill the holes. This resulted in a variation in the
cooling hole’s shape and diameter.
2.3.3 Location of the origin of damage and the Inspection area

4. 4
2.3.5 Inspection requirements to ensure safety and preclude liberation of blades:
Initial inspection was to be carried out before 500 Engine Cycles since new (CSN) and if the
engine has already crossed 500 CSN, inspection is to be carried out within 6 months.
Repeat Inspection to be carried out every 250 cycle interval thereafter.
The boroscope examination is to visually look for any sign of heat damage on the shrouds which
could result in further damage. Based on the extent of the progression of damage and the size of
the damage, repeat inspection intervals are further determined.
2.3.6 Terminating action:
Replacing the existing shrouds with the modified shrouds which have the cooling holes drilled
into it through a proven method by a procedure known as electric-discharge machining (EDM)
has an improved shroud cooling hole pattern, thereby restoring the shroud cooling to the design
intent.
2.4 My Role in Workplace Activity
I was heading a team of 5 maintenance planners in charge of Line Maintenance Planning for the
entire Boeing 777 fleet.
On an average, 3 engines had to be inspected to ensure the compliance of the requirement. This
inspection, depending on the extent of damage could result in engine removal as well. This
became a very big challenge since the aircraft would have to be taken out of operation for a
period of time causing significant impact on cost and to the regular scheduled operations in turn
leading to delay and passenger dissatisfaction.
2.4.1 Understanding the existing requirements – my knowledge and evaluation:
The project was implemented by –
 Daily meetings to evaluate the inspection report and photos to determine the next
inspection interval by considering the impact on operations.
o Example 1: If more than 3 engines were due for inspection on the same day, it
would be impossible to carry out the inspection together without affecting the
operations.
o Example 2: Two engines of the same aircraft cannot be inspected on the same day
due to the risk of both the engines being removed simultaneously. Dual engine
removals require a test flight as it is an Extended Range Operation for Twin
Engines (ETOPS) requirement which is a huge cost to the organization and also
implies that there should be 2 serviceable engines available in the engine shop for
replacement, which is almost impossible.
o Example 3: Two engines with a highly deteriorating LPT shroud cannot be
planned on the same day due to the risk of 2 engine removals at the same time.
 Analyzing the existing findings to arrive and determine the repeat inspection intervals.

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 Plan for engine removals in coordination with engine shop for the availability of engines.
 Providing data back to GE for their analysis and improving the inspection needs on a real
time basis.
 Measuring and understanding the location of the holes and size of the holes through
standard reference points.
 Negotiating for further extensions with the manufacturer to maximize operations based
on the slower deterioration pattern which was determined by repetitive inspections.
2.4.2 Inspection and Modification through precise planning:
With a new generation fleet size of Boeing 777 aircraft affected by this requirement equating to
154 Engines to be inspected, it required the following attributes in the role:
1. Due to the number of affected engines, there was an agreement with GE that they would
provide manpower for complete boroscope inspection. However the coordination of
inspection, data analysis and decision-making rested on me and my team.
2. This required very good planning skills where a monthly inspection plan had to be
developed in coordination with various other departments such as Engineering Technical
Services, Aircraft Scheduling, the General Electric (GE) field representatives and
inspection team. This had to be as accurate as possible to ensure minimum deviation from
the plan in order to have least impact to the operations and other stakeholders.
3. I devised the idea of the monthly inspection plan which formed the baseline for seamless
execution. However changes to the plan were made on a day-to-day basis based on the
review and analysis of the boroscope inspection findings and boroscope photos of the
affected engine.
4. Reviews and analysis of the damage helped me and the team to predict the time of engine
failure which enabled precise planning of an engine removal for permanent modification.
Decision-making and anticipation were key elements so that I could clearly communicate
with the Engine Shop team in advance to ensure the availability of the required number
of engines on time and also to give prior notice to the Aircraft Scheduling team to have
flexibility to allocate the necessary ground time without affecting operations.
5. This set the road map for repeat inspection and engine removal plans for permanent
modification.
2.5 Conclusion:
Besides my planning expertise, technical knowledge of the Boeing 777 (GE-90 115B) engine
and the inspection procedure were the primary skill requirements to execute this project. I also
had to coordinate with other departments of Emirates Engineering for successful completion.
The entire project was carried out with minimum effect on operations. The permanent
modifications on all the affected engines were made preemptively before any incident could
occur and closed the requirement of further inspection.