Frequency as airlines’ means to

accommodate growth, and

implications on e-taxiing

Terence Fan

terencefan@smu.edu.sg

Past: bigger aircraft was better

• Before the advent of revenue management and liberal air service

agreements, larger aircraft boosts airlines’ profit with their lower

per-seat costs

1

Source: https://qph.ec.quoracdn.net/main-qimg-ccfb5658c0f2e248b9e3a5add2f22084-c; http://aero.stanford.edu/bwbfiles/largeacopt.html

Now: better revenue management…

• lets airlines price-discriminate passengers, e.g., LHR-NRT-LHR on BA:

2

Source: Fan & Leung, Journal of Revenue & Pricing Management

…lets airlines ‘right-size’ capacity

• Based on the profile of airfare obtained ($ and demand), airlines

reduce their aircraft size in the long run to capture higher-

yielding traffic, and to increase frequency to capture growth

Operating surplus per flight, USD

From Fan, Journal of Transportation Research Forum

Profit maximizes at small aircraft size with price disparity & proper fare fencing3

Liberal policy + budget carriers → more flights

• That was the case for non-stop flights between UK &

Ireland, and continental Europe in the early 2000’s

Cumulative average

growth of 6%/year

Source: Fan, Journal of Transport Geography

4

Frequency growth at Changi (1)

• Disproportionate use of (smaller) narrow-bodies to

accommodate growth on existing routes ~ 1-2 hrs

14

95

18

0

20

40

60

80

100

120

140

160

180

200

2005 2015

SIN-Penang

Narrobody Widebody-ex747380

7

70

24

35

0

20

40

60

80

100

120

140

160

180

200

2005 2015

SIN-Denpasar

Narrobody Widebody-ex747380

62

112

107

83

7

0

20

40

60

80

100

120

140

160

180

200

2005 2015

SIN-Bangkok

Narrobody Widebody-ex747380

Widebody-747380

Weekly frequencies for 1-2.9 block hrs, Official Airline Guide

5

Frequency growth at Changi (2)

• Disproportionate use of (smaller) narrow-bodies to

accommodate growth even long routes of ~ 4 hrsWeekly frequencies for 3-5.9 block hours, Official Airline Guide

7

2924

18

0

20

40

60

80

100

120

140

2005 2015

SIN-Taipei

Narrobody Widebody-ex747380

12

79

30

35

0

20

40

60

80

100

120

140

2005 2015

SIN-Manila

Narrobody Widebody-ex747380

21

35

49

105

28

7

0

20

40

60

80

100

120

140

2005 2015

SIN-Hong Kong

Narrobody Widebody-ex747380

Widebody-7473806

Frequency growth at Changi (3)

• Disproportionate use of narrow-bodies to open new routes

2015 weekly frequencies for some cities not served from SIN in 2005, Official Airline Guide

1415

19

37

0

5

10

15

20

25

30

35

40

Krabi Hangzhou Tiruchirappalli Bandung 7

As no. of flights increase, delays soar• Sample no. of flights scheduled per hour at New York LaGuardia

Hours of the day

(e.g., 7 = 0700-0759)

8

0

20

40

60

80

100

120

5 7 9 11 13 15 17 19 21 23 1 3

Nov, 00

Aug, 01

81 flights/hour

0

10

20

30

40

50

60

70

80

90

5 7 9 11 13 15 17 19 21 23 1

ASQP actual

OAG+GA

OAG-

cancel+GA

0

10

20

30

40

50

60

70

80

90

5 7 9 11 13 15 17 19 21 23 1

ASQP actual

OAG+GA

OAG-

cancel+GA

Taxiing delay per departing flight (mins), Aug 01 Taxiing delay per departing flight (mins), Nov 00

A small increase in frequency at a

busy airport can lead to huge delays

...and simulation is realistic

• Sample flight delays at New York LaGuardia without slot control

0

10

20

30

40

50

60

70

80

90

5 7 9 11 13 15 17 19 21 23

OAG + GA

3-Nov-00

8-Nov-00

13-Nov-00

OAG + GA - Cancel

Taxi delay based on scheduled departure time (minutes/flight);

Delay ≡ (actual wheels-up time – actual pushback time) – 15 mins of standard taxiing out time

Simulated

Actual fine-

weather

days

Simulated

Hours of the day (e.g., 7 = 0700-0759)9

Situation for Asia & beyond

• Airport responses

– Stop-gap slot control*

– Longer-term capacity expansions

(more in Asia)

• Airline responses:

– Schedule creep/padding ($$$, see next)

– Potentially, more efficient taxiing

10

* See, e.g., Fan & Odoni, Journal of Air Traffic Control Quarterly for variations in practice

Schedule creep a fact of life

• Schedule creep

– Refers to the gradual increase in scheduled block times for the

same city-pairs over the years

– Route Past (year) 2015 (hr:min)

ORD (Chicago) – SFO 4:25 (’05) 4:43

ORD – LHR 7:49 (’10) 8:02

MDW (Chicago) – MSP 1:23 (’05) 1:27

LGA (NYC) – ORD 2:25 (’96) 2:55

LGA – IAH (Houston) 2:30 (’73) 4:10

– Overall, increase in block times:

• 18% worldwide in 1999-2009

• 4% to 6% worldwide in 2005-2015

11Source: http://www.chicagotribune.com/news/columnists/ct-airline-flight-times-getting-around-met-1207-20151214-column.html ;

http://www.telegraph.co.uk/travel/news/why-flight-times-are-getting-longer-fuel-flying-slower/;

http://www.businesstravelnews.com/Aviation/Schedule-Creep-Demand-Drop-Redefine-Air-Delays/12243

E-taxiing can stop

schedule creep

Schedule padding also a fact of life

• Schedule padding

– Scheduling longer-than-necessary scheduled block times,

with the potential aim of improving on-time performance

– Southwest’s example illustrates the fine line among shorter

scheduled block times, no. of aircraft required & on-time

performance

12Note: On-time defined by percent of flights arriving within 14:59 minutes of schedule

Source: https://www.dallasnews.com/business/airlines/2014/10/27/schedule-adjustments-put-southwest-airlines-on-time-performance-back-on-course

Aug 201312 months before 12 months after

Tightened schedule: removed equivalent

of 16 aeroplanes (out of 680)

80.2% on-time performance

Rank: 7th of 16 airlines

71.1% on-time performance

Rank: Tied for last

E-taxiing can help reduce schedule padding needed

• Based on the airport as a single-server, with a queue of departing and

arriving aircraft

Delay simulation principle

13

Airport

Departed or arrived aircraftQueue of departing and arriving aircraft

Legend: departing and arriving aircraft

It pays to be at the head of the queue,

and e-taxiing helps airlines get there

• Longer turnarounds, as necessitated by increased airport-related delays,

require more aircraft to operate the same schedule

Delays & turnarounds have big impact

14

Source: http://www.nytimes.com/2006/11/14/business/14boarding.html

2006 schedule with 2773 daily turnarounds

Actual schedule Add 5 mins to each turnaround

18 more 737s needed!

Number of aircraft needed479

461

Minutes saved from

each turnaround can

save a lot of $$$

• Longer engine start-up time contributes to longer turnaround

times – apparently a big turn-off

– PW1100G-JM engines on A320neos require longer start-up times,

from 150 seconds to 350 seconds in hot conditions (2-3 mins extra)

…same with slightly longer engine starts

15Sources: http://aviationweek.com/commercial-aviation/qatar-airways-cancels-more-a320neo-orders; http://aviationweek.com/commercial-aviation/indigo-impacted-a320neo-

startup-time-issues ; http://in.reuters.com/article/interglobe-results-idINKCN10C28Z; http://www.reuters.com/article/us-pratt-airbus-a-idUSKCN0VZ1KE

“The longer startup time required for cooling of the

PW1100G engines…is making it…difficult for IndiGo to

maintain flight schedules”

“Qatar Airways refused to take an aircraft…before … fixes

were installed to the PW1100G engines”

“The extra warm-up time creates problems for Lufthansa

because of a shortage of space to taxi at Frankfurt airport”

Taxiing takes up 19% of block hour

• Based on A320 fleet

– 12-month average till Apr 2012

– 1.8 hours/flight average gate-to-gate (‘block’) time

– 20 mins/flight spent on taxiing

– 8.9 hours/day daily utilisation

16

Source: <http://www.airbus.com/fileadmin/media_gallery/files/brochures_publications/FAST_magazine/FAST51.pdf> p.8, accessed 10 May 2017

19% of gate-to-gate time actually on taxiing!

3-min reduction in taxi time per flight translates

into a 15-min reduction in block time every day,

or ~2% reduction in scheduled crew expenses!

• While aircraft taxiing delays are difficult to obtain, short aircraft

turnaround times have been associated with increased profitability

Shorter turnarounds increase profits

17Note: Ground time of over 3 hours ignored; only narrow-bodies included; using FlightRadar24 data

Source: https://airinsight.com/2017/05/08/correlation-airline-ground-time-profits/

E-taxiing can reduce turnaround time

18

Source: Airport Cooperative Research Program Report 158: Deriving Benefits from Alternative Aircraft-Taxi Systems, Transportation Research Board,

2016, p.2, p.9, p.16, p.17

• Among various electric aircraft taxiing technologies,

– Dispatch taxiing (e.g., using existing pushback tractor)

– Semi-robotic dispatch taxiing (e.g., using a hybrid external tractor for taxiing)

– Nose-wheel-mounted electric aircraft taxiing systems

– Main landing gear electric aircraft taxiing systems

– Replacement of the APU with on-board taxi jet engine

• those without the need to attach and detach external systems can save

up to 2 minutes in push-back procedures

Plus, e-taxiing saves fuel (1)

19

Source: <http://www.airbus.com/fileadmin/media_gallery/files/brochures_publications/FAST_magazine/FAST51.pdf> p.6, p.8, accessed 10 May 2017

Up to 10% of fuel

burnt on ground

Plus, e-taxiing saves fuel (2)

20Source: <http://www.airbus.com/fileadmin/media_gallery/files/brochures_publications/FAST_magazine/FAST51.pdf>

p.9, accessed 10 May 2017

• Without the main engine thrust, e-taxiing reduces fuel burn and

associated emissions during taxiing

Conclusion

• As passenger air transport demand increases,

– capacity-related delays will soar,

– schedule padding and creep will be a fact of life

– seconds shaved off the usual taxiing process or turnarounds

matter!

– efficient e-taxiing can give one airline an important

advantage, leading to increased profits, against others

• To improve airline and airport planning:

– need better operational data for analysis

21

Summary

• Economics encourages airlines to use frequency to

accommodate growth

• In the world of increasing flight delays,

– The U.S. experience (no slot control) shows that being able

to get to head of take-off/landing queues can save a lot of

time & costs

– Experience from Asia (with slot control) shows relentless

rise in frequency, bearing some similarity to the U.S.

experience

• E-taxiing

– Better able to place an airline’s aeroplane at head of take-

off queues to save time & cost22