1.
Commercial aircraft operation
engine realibility & safety
Olivier Petit & Henrik Ekstrand
Applied Mechanics department, fluid mechanics division
01/12/2022 AoA Transport Lunch Seminar

2.
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Background
There is a market pull to fly further and further away.
Average of 6 000 – 10 000 planes in the sky at any time. (expected 5% per
year increase for the coming 10 years)
Need for regulations to avoid accidents, and manage take-off and landings.
Creation of highways in the sky to avoid collision.

3.
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Aviation safety
A wide topic where interaction typically occurs between all stakeholders
(e.g. Airspace Users (AUs), Air Navigation Service Providers (ANSPs),
Airport Operators etc.).
Airspace Users typically has great redundancy in various systems (e.g.
three hydraulic systems).
Communication, Navigation & Surveillance (CNS).
ANSPs and AUs are using various surveillance systems for traffic
sequencing and separation, including airborne anti collision systems such
as the Traffic Collision Avoidance System (TCAS).
Satellite navigation used as primary navigation source associated with
very high accuracy.
Communication is established all around the world via ground stations or
SatCom.

4.
1
2.03
3.36
4.97
6.84
8.94
0
1
2
3
4
5
6
7
8
9
10
1000 1500 2000 2500 3000 3500
Failure
probability
per
10
000
hours
Engine horsepower
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8.12
10.08
13.68
0
2
4
6
8
10
12
14
16
1500 2000 3000
Failure
probability
per
10
000
hours
for
6
000
HP
Failure probabilities 6 000 HP installed
1953 data from ICAO(International Civil Aviation Organisation)
Early airplanes were powered by piston engine. The reliability of piston engine at the time was rather poor.
There is a close correlation between engine failure and engine power (see left picture).
As a consequence, a 60 minute rule was established In 1953: to always operate an aircraft within 100 NM
from an adequate airport (100 NM ≈ 60 min flying with one engine inoperative).
1 NM (Nautical Mile=1.852 km)
Probability of failure for piston engines vs.
power at a constant engine speed of 1 000 rpm.

5.
01/12/2022 AoA Transport Seminar 5
Reliability of jet engines since the 1950s and onwards
The introduction of jet engines significantly enhanced the reliability and safety of propulsion
systems.
The failure probability of a jet engine in neither affected by the thrust nor by the size of the
engine.
In today’s operation it is possible to operate > 180 minutes from an adequate airport with a twin
engine aircraft (based on single engine operation).
0
0.002
0.004
0.006
0.008
0.01
0.012
22-30 37-40 48-50 50-60 65-70+
Failure
rate
per
1000
hours
Engine thrust (kilo Pounds)

6.
ETOPS certification operational since 1985
(ETOPS-90, ETOPS-120)
ETOPS definition: extended range operations
are those flights conducted over a route that
contain a point further than one hour flying time
at the approved one-engine inoperative cruise
speed (under standard conditions in still air)
from an adequate airport.
Combined safety measure, EROPS: En Route
Alternate Airports. It denotes that this airport is
adequate for use as an ETOPS alternate
(weather, runway length, wide and strength…).
Military airports are available as En Route
Alternate.
01/12/2022 AoA Transport Seminar 6
ETOPS certification: Extended-range Twin engine OPerationS
ETOPS certification representation

7.
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180 min operation
Operational impact
120 min operation
Direct route = 4350 NM 60 min rule = 5700 NM 180 min rule = 4350 NM

8.
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Engine certification
There are hundreds of tests that need to be
performed for certification of a turbine engine.
Amongst them are:
Maximum static thrust tests
Vibration tests
Endurance tests
Water ingestion test
Hail ingestion test
Ice cloud test
Bird strike test

9.
Engine certification:
electronic code of federal regulations: http://www.ecfr.gov/cgi-bin/text-idx?rgn=div5&node=14:1.0.1.3.16#_top
01/12/2022 AoA Transport Seminar 9

10.
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Engine certification:
electronic code of federal regulations: http://www.ecfr.gov/cgi-bin/text-idx?rgn=div5&node=14:1.0.1.3.16#_top

11.
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Aviation statistics
Boeing Statistical Summary of Commercial Jet Aircraft
Accidents 1959-2015
You can travel 7 times to the moon or 14 000 times around the globe before experiencing an emergency
landing to En Route Alternate Airports.
There were four accidents resulting in passenger fatalities in 2015, all of which involved turboprop aircraft,
with 136 fatalities. This compares with an average of 17.6 fatal accidents and 504 fatalities per year in the
previous five-year period (2010-2014).
IATA: International Air Transport Association, trade association for the
world’ airlines

12.
Thank you for your attention!
01/12/2022 AoA Transport Seminar 12