Third-Quarter 2003 — July AERO 3

VAN CHANEYFLIGHT TEST PILOT

FLIGHT OPERATIONS PRODUCTIONBOEING COMMERCIAL AIRPLANES

MIGUEL SANTOSDIRECTOR

INTERNATIONAL SALESBOEING COMMERCIAL AIRPLANES

ALLEN ROHNERREGIONAL DIRECTOR

MARKETINGBOEING COMMERCIAL AIRPLANES

In the kingdom of Bhutan, high in the HimalayanMountains, is Paro International Airport. One of the world’smost challenging airports, Paro is 7,300 ft (2.23 km)above sea level and surrounded by deep valleys and18,000-ft (5.48-km) peaks. Here a Boeing 737-700recently completed successful technical demonstrationtest flights that proved its performance capabilities andverified procedures for safe takeoff and landing opera-tions in high-elevation, high-terrain environments.

F L I G H T O P E R A T I O N S

BUZZ NELSONCHIEF PROJECT PILOT

FLIGHT OPERATIONSBOEING COMMERCIAL AIRPLANES

MAGALY CRUZPERFORMANCE, AERODYNAMICS ENGINEER

FLIGHT OPERATIONS ENGINEERINGBOEING COMMERCIAL AIRPLANES

JAMES WILSONPERFORMANCE, AERODYNAMICS ENGINEER

SALES SUPPORT AERODYNAMICSBOEING COMMERCIAL AIRPLANES

737-700737-700BHUTANBHUTANTECHNICAL DEMONSTRATION FLIGHTS INTECHNICAL DEMONSTRATION FLIGHTS IN

Third-Quarter 2003 — July4 AERO

TECHNICAL DEMONSTRATIONTEST FLIGHT AIRPLANE

The demonstration airplane was a 737-700 Boeing Business Jet (BBJ)configured with blended winglets and abusiness jet interior (fig. 1 and table 1).The 737-700 BBJ used for the demon-stration flights is aerodynamicallyequivalent to the commercial variant ofthe 737-700 being offered to Druk Air.

TECHNICAL DEMONSTRATIONTEST FLIGHTS DESCRIPTION

On February 6, 2003, two technicaldemonstration test flights were ac-complished from runways 33 and 15

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1aro International Airport,in the kingdom of Bhutan,is high in the Himalayan

Mountains. At 7,300 ft (2.23 km)above sea level, with a runway6,500 ft (1.99 km) long, surroundedby deep valleys and 18,000-ft (5.48-km) peaks, Paro is one of theworld’s most difficult airports fortakeoffs and landings.

In February 2003, a Boeing 737-700 successfully completed 11 test flights at Paro InternationalAirport. The series included twotechnical demonstration flights andeight customer relations flights withDruk Air Royal Bhutan Airlines, thenational airline of Bhutan. Druk Air,which operates two 72-passengerBAe 146-100 jets from Paro to sixcities in five countries, is consider-ing upgrading its fleet and extendingits routes. The rigorous test flightsproved that the 737-700 is capableof meeting all performance and procedural requirements for safeoperations at Paro and other airportsin high-elevation, high-terrain environments.

The 737-700 performed flightmaneuvers as predicted and met orexceeded performance expectationsfor simulated one-engine-inoperativemaneuvers, which were accomplishedby reducing thrust on one engine to idle power. The expected perform-ance levels proved conservative whencompared with the demonstrated performance of the 737-700.

Test flight data were verified by flight data recorder (FDR) infor-mation, indicating that predicted airplane performance is represen-tative of actual airplane performance as recorded by the FDR.

The test flights verified proceduresfor takeoff and landing operations at Paro. The 737-700 demonstrated

engine-out takeoff procedures, whichis required for Paro operations,engine-out missed approach and go-around procedures, and Druk Airprocedures for landing on both directions of the runway at Paro.

This article discusses

1. Technical demonstration test flight airplane.

2. Technical demonstration test flights description.

3. Technical demonstration test flight analysis.

P

Golmud

Hotan

Lhasa

Imphal

Sholapur

Mandalay

Sit twe

Monywa

Dhaka

Thimphu

Paro

New Delhi

Rangoon

Kathmandu

INDIA

CHINA

MYANMAR

NEPAL

BHUTAN

BANGLADESH

Bay of Bengal

The kingdom of Bhutan is located near Nepal, between China in the north and India in the east, south, and west. The kingdom,which is roughly the size of Switzerland, has a population of750,000 people. The Bhutanese value their rich natural environ-ment and ecosystem, which includes 770 species of birds and 5,500 species of plants.

2

AERO 5Third-Quarter 2003 — July

at Paro International Airport. Boeingpilots Captain Buzz Nelson andCaptain Van Chaney flew the 737-700accompanied by the Druk Air chiefpilot on the first flight and a senior first officer on the second flight.

To prove the capability of the 737-700 at Paro, the technical demon-stration flights had to show that theairplane could take off following asimulated single engine failure at themost critical point during the takeoffground roll (V1) and safely return to the airport on one engine.

Terrain in the valleys surroundingParo limits takeoff performance. Flight operations into and out of Paroonly occur when the visibility in the valley is clear. This visibility is required to allow an airplane to turnaround safely within the steep valleywalls and reach the minimum safe alti-tude to depart the valley or return to theairport in the event of an engine failure.

The technical demonstration flightprofile consisted of a takeoff with a simulated single engine failure at V1, a turnback within the river valley,a missed approach, a go-around,

a turnback at the opposite end of the valley, and landing, with one engineremaining at idle (representing theengine failure) throughout the demonstra-tion. One technical flight demonstrationwas accomplished in each directionfrom the runway at Paro.

Runway 33 Technical Demonstration Test FlightThe first technical demonstration testflight was performed from runway 33(fig. 2). After takeoff, a right bank was initiated for a heading change of

approximately 30 deg to avoid terrainthat extends from the west valleywall. This maneuver was followed bya left bank to position the airplanealong the east wall of the west forkof the river. The climb continuedclose to the east wall until the turn-back initiation point. A teardrop turnback was initiated just after passing abeam the Chhukha village.Here the terrain falls away off theright wing where a stream emptiesinto the river. The turnback wasflown with a 30-deg bank whilemaintaining speed throughout

the turn.After completing the teardrop

maneuver, the pilots performeda flaps 15 (engine-out landing flap)missed approach to runway 15. Thiswas followed by a go-around and ateardrop turnback south of the runwayusing the Druk Air runway 15 turn-back procedure. The condition wascompleted successfully with a normalflaps 40 landing using the Druk Airstraight-in landing procedure.

The takeoff weight for runway 33 islimited by the turning radius required

Boeing 737-700 BBJ

N184QS

30884

171,500 lb (77,791 kg)

171,000 lb (77,564 kg)

134,000 lb (60,781 kg)

126,000 lb (57,153 kg)

9,700 U.S. gal (36,718 L)

CFM56-7B

Airplane model

Registration number

Manufacturer’s serial number

Maximum taxi weight

Maximum takeoff weight

Maximum landing weight

Maximum zero fuel weight

Fuel capacity

Engines

DEMONSTRATION AIRPLANE SPECIFICATIONS

TABLE

1

737-700 TECHNICAL FLIGHT DEMONSTRATION AIRPLANE

FIGURE

1

6 AERO Third-Quarter 2003 — July

to perform a 30-deg bank turnback.The available turning radius is basedon the valley width at the net heightachievable while maintaining not less than 492 ft (150 m) of lateralseparation to the terrain and all ob-stacles on either side of the intendedtrack. The limit weight calculationswere based on the valley width at the net height for turnback initiation,

assuming that the airplanewas positioned within 492 ft (150 m) of the valley wall.

The takeoff gross weight forthe technical demonstrationwas calculated based on theairplane empty weight and theweight of the crew, passengers,and fuel on board (table 2).Table 3 lists the airport con-ditions and airplane configu-ration and takeoff speeds.

Engine failure was simulated bythrottling back the left engine to idle at 125 kias, the V1 speed for takeoff.

Runway 15 Technical Demonstration Test FlightThe second technical demonstration test flight was performed from runway 15 (fig. 3).

After liftoff, a right bank was per-formed for a 10-deg heading change,followed by a left bank for a 60-deg

Brake release

Landing

Runway33

Runway15

Takeoff

1,200 ft

1,200 ft

1,200 ft540 ft

540 ft

540 ft

6,000

4,000

2,000

0

-2,000

-4,000

-6,000-8,000 -6,000 -4,000

Late

ral d

ispl

acem

ent f

rom

runw

ay c

ente

rline

, m

-2,000 0 2,000 4,000 6,000 8,000 10,000

Distance from brake release, m

Takeoff weight: 115,633 lb (52,450 kg) at 7°C V1, 125 kias; VR, 130 kias; V2, 136 kiasFlaps 5 takeoffFlaps 15 missed approach and go-aroundFlaps 40 landingAir conditioning off; anti-ice off

Contour heightsabove airport elevation

PARO RUNWAY 33 TECHNICAL DEMONSTRATION TEST FLIGHT OVERVIEW

FIGURE

2

*Includes the weight of three crewmembers, ten passengers, amenities, and potable water.

Runway 33

Runway 15

Zero fuel weight* 100,433 lb (45,556 kg)

Fuel 15,200 lb (6,895 kg) Takeoff weight 115,633 lb (52,450 kg)

Zero fuel weight* 100,433 lb (45,556 kg)

Fuel 13,900 lb (6,305 kg)

Takeoff weight 114,333 lb (51,861 kg)

DEMONSTRATION AIRCRAFTTAKEOFF GROSS WEIGHT

TABLE

2

Airplane configurationTakeoff gross weight: 115,633 lb (52,450 kg)Takeoff thrust rating: CFM56-7B26Center of gravity: 18.1%MACStab trim: 5.25 unitsFlaps 5 takeoffFlaps 15 missed approach and go-aroundFlaps 40 landingAir conditioning off; anti-ice off Left engine pulled to idle at V1

Airport conditionsTakeoff time: 03:58 ZuluLanding time: 04:10 ZuluTower-measured temperature: 7°CTower QNH: 1,021 mbar = 7,140 ft pressure altitudeTower wind: 190 deg at 6 kn

Airplane takeoff speeds

V1, 125 kias; VR, 130 kias; V2, 136 kias

PARO RUNWAY 33 TEST FLIGHT PARAMETERS

TABLE

3

AERO 7Third-Quarter 2003 — July

LandingTakeoff

Runway33

Runway15

1,200 ft

1,200 ft

1,200 ft

540 ft

540 ft

540 ft

6,000

4,000

2,000

0

-2,000

-4,000

-6,000-8,000 -6,000 -4,000

Late

ral d

ispl

acem

ent f

rom

runw

ay c

ente

rline

, m

-2,000 0 2,000 4,000 6,000 8,000 10,000

Distance from brake release, m

Takeoff weight: 114,333 lb (51,861 kg) at 9°C V1, 124 kias; VR, 130 kias; V2, 136 kiasFlaps 5 takeoffFlaps 15 missed approach, go-around, and landingAir conditioning off; anti-ice off

Contour heightsabove airport elevation

Brake release

PARO RUNWAY 15 TECHNICAL DEMONSTRATION TEST FLIGHT OVERVIEW

FIGURE

3

heading change. The left bank took theairplane across the valley toward theeast wall and avoided a hill that extendsfrom the west wall of the valley.

A right bank was then held for an approximate 95-deg heading change,which directed the airplane from theeast side of the valley back toward thewest side and the Silung Nang village.The airplane flew over Silung Nang and the ridge behind it, which requiredan altitude of 9,100 ft (2.77 km). After the airplane cleared the ridge,a turnback was initiated with a 30-degbank while maintaining the designatedV2 speed.

After completing the turnbackmaneuver, the pilots performed aflaps 15 (engine-out landing flap)missed approach to runway 33, fol-lowed by a go-around and a teardropturnback north of the runway usingthe runway 33 turnback procedure.The condition was completed

successfully with a normal flaps 15 landing using the Druk Air straight-inlanding procedure on runway 15.

The turnback procedure limit for runway 15 originally was deter-mined to be the turning radiusrequired to perform the 30-deg bankturnback. This limit was based on the valley width at the net heightachieved while maintaining a mini-mum 492-ft (150-m) splay outside the intended track.

However, before the technicaldemonstration flights, Boeing and Druk Air pilots flew practice flights.After these flights, the pilots deter-mined that the critical requirement wasclearing the ridge beyond the village of Silung Nang, which requires a netheight of 9,100 ft (2.77 km) at the turn initiation point. The limit weightcalculations were based on therequirement to achieve this height onthe net flight path. The turn radius

Airplane configurationTakeoff gross weight: 114,333 lb (51,861 kg)Takeoff thrust rating: CFM56-7B26Center of gravity: 18.1%MACStab trim: 5.25 unitsFlaps 5 takeoffFlaps 15 missed approach, go-around, and landingAir conditioning off; anti-ice offRight engine pulled to idle at V1

Airport conditionsTakeoff time: 04:22 ZuluLanding time: 04:30 ZuluTower-measured temperature: 9°CTower QNH: 1,020 mbar = 7,140 ft pressure altitudeTower wind: 140 deg at 6 kn

Airplane takeoff speeds

V1, 124 kias; VR, 130 kias; V2, 136 kias

PARO RUNWAY 15 TEST FLIGHT PARAMETERS

TABLE

4

Third-Quarter 2003 — July8 AERO

was not limiting at this condition,assuming a 30-deg bank.

Table 2 shows the airplane takeoffgross weight for the runway 15 tech-nical demonstration flight. Table 4 lists the airport conditions and airplane configuration and takeoff speeds.

Engine failure was simulated bythrottling back the right engine to idle at 124 kias, the V1 speed for takeoff.

TECHNICAL DEMONSTRATIONTEST FLIGHT ANALYSIS

FDR AnalysisFDR information was downloadedfrom the airplane after the technicaldemonstration test flights. The FDRflight paths were compared with profiles of predicted performance to

verify the capability to match actualflight profiles.

Figures 4 and 5 show the groundtracks and altitude profiles for thedemonstration test flights from runways33 and 15, respectively. The calcu-lated flight paths with one enginepulled back to idle thrust closelymatch the demonstrated flight paths.

3,000

1,000

-1,000

-3,000

-5,000

La

tera

l dis

plac

emen

t fro

m ru

nway

cen

terli

ne, m

9,000

8,000

7,000 4,000 2,000 0 -2,000 -4,000 -6,000 -8,000 -10,000-12,000

4,000 2,000 0 -2,000 -4,000 -6,000 -8,000 -10,000-12,000

Baro

met

ric a

ltitu

de, f

t

Distance from liftoff end, m

Distance from liftoff end, m

Brakerelease

Liftoff

Data from flight data recorderPredicted data, one engine at idle

Outbound terrain within 150 m

1,200 ft

1,200 ft

540 ft

540 ft

940 ft

1,070 ft

Runway33

Runway15

Chhukha

Contour heightsabove airport elevation

PARO RUNWAY 33 TEST FLIGHT GROUND TRACK AND ALTITUDE PROFILE

FIGURE

4

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The calculated altitudes at the turnback initiation points for both flights werewithin 50 ft (15 m) on the conservativeside of the predicted altitudes.

Turn Procedure OptimizationFor the technical demonstration testflight from runway 15, takeoff weightwas limited by the Druk Air proce-dural requirement to fly over a ridgeafter flying south over Silung Nang. To clear the ridge, a net altitude of 9,100 ft (2.77 km) is necessary at

the turn initiation point.Flying parallel to the valley wall

near Silung Nang instead of crossingthe ridge removes the requirement toreach 9,100 ft (2.77 km) and allows a greater takeoff weight. The perfor-mance then becomes limited by the width of the valley. Through carefulselection of the turn initiation point,additional takeoff weight is possible.

The available turn radius as a function of altitude was determined by computing the maximum turn

radius available in the valley at eachaltitude line on a digitized topographymap. Maximum takeoff weight wascalculated by plotting the available turn radius and the turn radius required as a function of gross takeoff weight.

Figure 6 is an example takeoffweight calculation. The bottom plotshows the airplane altitude at the turn initiation point. The middle plot shows the corresponding airspeeds. The top plot shows the turn diameterrequired for a 30-deg bank, which

Brakerelease

Predicted data, one engine at idleData from flight data recorder

4,000

2,000

0

-2,000

-4,000 14,000 12,000 10,000 8,000 6,000 4,000 2,000 0 -2,000

1,200 ft

1,200 ft

540 ft

540 ft

Silung Nang

La

tera

l dis

plac

emen

t fro

m ru

nway

cen

terli

ne, m

Outbound terrain within 150 m

11,000

9,000

7,000

Baro

met

ric a

ltitu

de, f

t

14,000 12,000 10,000 8,000 6,000 4,000 2,000 0 -2,000

Distance from brake release, m

Distance from brake release, m

Runway33

Runway15

Contour heightsabove airport elevation

PARO RUNWAY 15 TEST FLIGHT GROUND TRACK AND ALTITUDE PROFILE

FIGURE

5

10 AERO Third-Quarter 2003 — July10 AERO

is solely a function of true airspeed and bank angle, and the turn diameteravailable at the correspondingnet height.

Boeing continues to investigateproduct and operational improvements

10,000

11,000

12,000

7,000

Gross weight, lb

8,000

9,000

155

160

165

140

145

150

2,000

130

135

1,9001,800

10,800 110,000 112,000 114,000

Gross height

Net height

116,000 118,000 120,000 122,000

1,7001,6001,5001,4001,3001,200

Druk Air BAe 146 minimum altitude

ktas

kias

Diameter available at gross height

Diameter available at net height

Diameter required for 30-deg bank*

Diameter required for 35-deg bank*

*Assumes a 150-m splay on each side of intended track

Airs

peed

Turn

dia

met

er re

quire

d/av

aila

ble,

ftHe

ight

abo

ve a

irpor

t at t

urn

initi

atio

n, ft

Flaps 5 takeoffAir conditioning off; anti-ice offForward center of gravityNo windEngine failure at V1

PARO TAKEOFF WEIGHT CALCULATION

FIGURE

6

as part of its commitment to ensure that current and potential customerscan maximize payload capability during safe takeoff and landing opera-tions in high-elevation, high-terrain environments.

S U M M A R Y

Editor’s note: Druk Air Royal Bhutan Airlines only operates BAe 146-100 jets at this time; Boeing is not maximizing the payload capability of the BAe jets.

The success of rigorous tech-nical demonstration test flights at Paro International Airport inBhutan validated the capabilityof the Boeing 737-700 to perform as predicted in a high-elevation, high-terrainenvironment.

The test flight data demon-strate that the 737-700■ Met or exceeded performance

expectations for simulated one-engine-inoperative flight maneuvers, provingthat predicted performance is representative of actualperformance as recorded by the FDR.

■ Verified procedures for safetakeoff and landing opera-tions at Paro, one of theworld’s most challengingairports.

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IMPORTANCE OF SPEED DURINGTAKEOFF TURNBACK PROCEDURESProper speed is essential when flying takeoff turnback procedures. Lower speeds decrease the climb capability and thereby reduce terrainclearance. Higher speeds increase the turn radiusand bring the airplane closer to valley walls.

The pilots had the option of overbanking to stick-shaker speed or the initial buffet speed toachieve a smaller turn radius. They also could have combined pitch and roll to trade speed for altitude and reduced turn radius. Although thesemaneuvers are non-normal and were beyond the scope of this study, the pilots discussed their potential use to avoid terrain in an emer-gency or in high, unexpected cross-canyon wind conditions.

Optimal performance was achieved during the takeoffs from Paro by accelerating the airplane to a speed that was 10 kias faster than the minimum safety takeoff speed (10 kias ofimproved climb). This allowed for 30 deg of bankangle and provided the climb gradient necessary to initiate the turnback.

TAKEOFF CAPABILITYREFINEMENTAfter the technical demon-strations, several performanceoptions were studied toimprove the takeoff weightcapability from Paro. Theseincluded additional optimiza-tion of the turn procedures,increased takeoff thrust, use of alternate forward center ofgravity positions, and instal-lation of a weather station to allow use of Druk Air procedures B and C for runway 15. Using these procedures, the 737-700 can take off from Paro with114 passengers and 4,850 lb(2,200 kg) of payload. Otherenhancements that were stud-ied, such as potential runwayextensions and the removal ofobstacles surrounding the air-port, will further improve safeoperation at Paro.

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The technical flight demonstrations were performed using the CFM56-7B26thrust rating, which currently is the highest thrust rating certified on the 737-700. A new thrust bump rating,

CFM56-7B26/B2, hasbeen offered to Druk Air as a new product. The CFM56-7B26/B2thrust rating will

produce at least 2% more thrust thanthe CFM56-7B26 rating at the ParoInternational Airport elevation. The additional thrust is worth approximately2,100 lb (953 kg) of additional takeoffgross weight at Paro.

Takeoff gross weight can be increasedfurther by using the optimal airplanetakeoff center of gravity (CG) locationinstead of the conservative forward-limitlocation specified by the standard air-plane flight manual (AFM). The increaseis achieved by using the AFM-alternateCG takeoff performance option on the 737-700, which allows the operatorto select one of two specified CG locations. Using CG locations aft of the forward limit decreases airplanedrag and lowers stalling speeds, therebyincreasing takeoff performance. Forexample, using a 23%MAC CG locationinstead of the forward-limit location for

INCREASE TAKEOFF GROSS WEIGHT USING CFM56-7B26/B2 THRUST RATING AND ALTERNATE CENTER OF GRAVITY

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runway 15 increases 737-700 takeoffgross weight by 1,200 lb (544 kg).

Airport conditions and terrain constraints limited the demonstrationtakeoff gross weight to approximately115,000 lb (52,163 kg). However,by optimizing the turn procedures and using the CFM56-7B26/B2 thrustrating and alternate CG performance,takeoff gross weights in excess ofapproximately 120,000 lb (54,431 kg)are achievable. This improvement wouldallow Druk Air to fly a 737-700 with a full passenger payload from Paro to all its current initial destinations.

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Allen Rohner is regional director of marketing for countries in the Indian Ocean, Indian subcontinent, and Africa. In his 30 years atBoeing, Allen has held technical analyst positions in aerodynamicsengineering, working on the 747, 767, and 777 programs in salesand marketing support and product development. Allen was key infacilitating and organizing the effort that made the technical demon-stration test flights in Bhutan happen.

Capt. Van Chaney has almost 20 years of aircraft testingexperience, both as a test pilot and an aerospace engineer. A 737 and 757 pilot, Van has worked at Boeing for seven yearsand conducts research in the company’s H-295 Helio Courier andCessna 206. He is a member of the Society of Experimental TestPilots and has authored several professional papers.

Miguel Santos is director of international sales forcountries in Asia and Africa. During his 24-year career with Boeing, he has held engineering and managementpositions in advanced engineering, marketing, sales support engineering, marketing management, customerrequirements, and sales organizations. Miguel has bachelor’s and master’s degrees in aerospace engineering and an MBA.

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About the Authors

Magaly Cruz is a performance engineer with five years of experience in aerodynamics. Magaly was instrumentalin developing takeoff procedures for theParo technical demonstration flights.

Capt. Buzz Nelson has flown more than 14,000 flight-hours during his 40-year aviation career. He is qualified on all models of the 737, 747, 757, 767, and 777 and has been involved in their development and certification programsduring his 30 years with Boeing. For almost 10 years, Buzz was a member of the Society of Automotive Engineers S-7 committee, which writes design practices for the handlingqualities of large commercial airplanes and flight deck designs.

James Wilson, lead engineer, supports the sales of all Boeing airplane models by providing aerodynamic performanceinformation. During his 18 years with Boeing, James hasworked in aerodynamics on 747-400 certification, 747 and 767 fleet support, and 747, 767, and 777 fuel mileage.