In the kingdom of , high in the Himalayan Mountains, is Paro . One of the world’s most challenging airports, Paro is 7,300 ft (2.23 km) above sea level and surrounded by deep valleys and 18,000-ft (5.48-km) peaks. Here a 737-700 recently completed successful technical demonstration test flights that proved its performance capabilities and verified procedures for safe takeoff and landing opera- tions in high-elevation, high-terrain environments.

FLIGHT OPERATIONS

VAN CHANEY FLIGHT TEST PILOT FLIGHT OPERATIONS PRODUCTION BOEING COMMERCIAL AIRPLANES

MAGALY CRUZ PERFORMANCE, AERODYNAMICS ENGINEER FLIGHT OPERATIONS ENGINEERING BOEING COMMERCIAL AIRPLANES

BUZZ NELSON CHIEF PROJECT PILOT FLIGHT OPERATIONS 737-700737-700 BOEING COMMERCIAL AIRPLANES TECHNICALTECHNICAL DEMONSTRATIONDEMONSTRATION FLIGHTSFLIGHTS ININ ALLEN ROHNER REGIONAL DIRECTOR MARKETING BOEING COMMERCIAL AIRPLANES

MIGUEL SANTOS DIRECTOR INTERNATIONAL SALES BHUTANBHUTAN BOEING COMMERCIAL AIRPLANES

JAMES WILSON PERFORMANCE, AERODYNAMICS ENGINEER SALES SUPPORT AERODYNAMICS BOEING COMMERCIAL AIRPLANES Third-Quarter 2003 — July AERO 3 aro International Airport, engine-out takeoff procedures, which 1 TECHNICAL DEMONSTRATION P in the kingdom of Bhutan, is required for Paro operations, TEST FLIGHT AIRPLANE is high in the Himalayan engine-out missed approach and The demonstration airplane was a Mountains. At 7,300 ft (2.23 km) go-around procedures, and 737-700 Boeing Business Jet (BBJ) above sea level, with a procedures for landing on both configured with blended winglets and a 6,500 ft (1.99 km) long, surrounded directions of the runway at Paro. business jet interior (fig. 1 and table 1). by deep valleys and 18,000-ft This article discusses The 737-700 BBJ used for the demon- stration flights is aerodynamically (5.48-km) peaks, Paro is one of the 1. Technical demonstration equivalent to the commercial variant of world’s most difficult airports for test flight airplane. the 737-700 being offered to Druk Air. takeoffs and landings. In February 2003, a Boeing 2. Technical demonstration 2 TECHNICAL DEMONSTRATION 737-700 successfully completed test flights description. TEST FLIGHTS DESCRIPTION 11 test flights at Paro International On February 6, 2003, two technical 3. Technical demonstration Airport. The series included two demonstration test flights were ac- test flight analysis. complished from runways 33 and 15 technical demonstration flights and eight customer relations flights with Druk Air Royal Bhutan , the Hotan Golmud national of Bhutan. Druk Air, which operates two 72-passenger CHINA BAe 146-100 jets from Paro to six cities in five countries, is consider- ing upgrading its fleet and extending its routes. The rigorous test flights proved that the 737-700 is capable BHUTAN Lhasa of meeting all performance and procedural requirements for safe Paro New operations at Paro and other airports in high-elevation, high-terrain environments. Imphal The 737-700 performed flight maneuvers as predicted and met or exceeded performance expectations Monywa for simulated one-engine-inoperative Mandalay maneuvers, which were accomplished Sittwe by reducing thrust on one engine to idle power. The expected perform- Sholapur ance levels proved conservative when Rangoon compared with the demonstrated performance of the 737-700. Bay of Bengal Test flight data were verified by flight data recorder (FDR) infor- mation, indicating that predicted airplane performance is represen- The kingdom of Bhutan is located near Nepal, between China tative of actual airplane performance in the north and India in the east, south, and west. The kingdom, as recorded by the FDR. which is roughly the size of Switzerland, has a population of The test flights verified procedures 750,000 people. The Bhutanese value their rich natural environ- for takeoff and landing operations ment and ecosystem, which includes 770 species of birds and at Paro. The 737-700 demonstrated 5,500 species of plants.

4 AERO Third-Quarter 2003 — July 1 737-700 TECHNICAL FLIGHT DEMONSTRATION AIRPLANE FIGURE

at Paro International Airport. Boeing DEMONSTRATION AIRPLANE approximately 30 deg to avoid terrain pilots Captain Buzz Nelson and 1 SPECIFICATIONS that extends from the west valley Captain Van Chaney flew the 737-700 TABLE wall. This maneuver was followed by accompanied by the Druk Air chief Airplane model Boeing 737-700 BBJ a left bank to position the airplane pilot on the first flight and a senior Registration number N184QS along the east wall of the west fork first officer on the second flight. Manufacturer’s serial number 30884 of the river. The climb continued To prove the capability of the close to the east wall until the turn- 737-700 at Paro, the technical demon- Maximum taxi weight 171,500 lb (77,791 kg) back initiation point. A teardrop stration flights had to show that the Maximum takeoff weight 171,000 lb (77,564 kg) turnback was initiated just after airplane could take off following a Maximum landing weight 134,000 lb (60,781 kg) passing abeam the Chhukha village. simulated single engine failure at the Here the terrain falls away off the Maximum zero fuel weight 126,000 lb (57,153 kg) most critical point during the takeoff right wing where a stream empties Fuel capacity 9,700 U.S. gal (36,718 L) ground roll (V1) and safely return into the river. The turnback was to the airport on one engine. Engines CFM56-7B flown with a 30-deg bank while Terrain in the valleys surrounding maintaining speed throughout Paro limits takeoff performance. a turnback at the opposite end of the the turn. Flight operations into and out of Paro valley, and landing, with one engine After completing the teardrop only occur when the visibility in remaining at idle (representing the maneuver, the pilots performed the valley is clear. This visibility is engine failure) throughout the demonstra- a flaps 15 (engine-out landing flap) required to allow an airplane to turn tion. One technical flight demonstration missed approach to runway 15. This around safely within the steep valley was accomplished in each direction was followed by a go-around and a walls and reach the minimum safe alti- from the runway at Paro. teardrop turnback south of the runway tude to depart the valley or return to the using the Druk Air runway 15 turn- airport in the event of an engine failure. Runway 33 Technical back procedure. The condition was The technical demonstration flight Demonstration Test Flight completed successfully with a normal profile consisted of a takeoff with The first technical demonstration test flaps 40 landing using the Druk Air a simulated single engine failure at flight was performed from runway 33 straight-in landing procedure. V1,a turnback within the river valley, (fig. 2). After takeoff, a right bank The takeoff weight for runway 33 is a missed approach, a go-around, was initiated for a heading change of limited by the turning radius required

Third-Quarter 2003 — July AERO 5 2 PARO RUNWAY 33 TECHNICAL DEMONSTRATION TEST FLIGHT OVERVIEW FIGURE 6,000 Takeoff weight: 115,633 lb (52,450 kg) at 7°C V1, 125 kias; VR, 130 kias; V2, 136 kias Flaps 5 takeoff Flaps 15 missed approach and go-around Flaps 40 landing 4,000 1,200 ft Air conditioning off; anti-ice off

540 ft 2,000

1,200 ft 540 ft Runway Runway 15 33 0 Landing Takeoff Brake release

-2,000 Contour heights 540 ft 1,200 ft above airport elevation -4,000 Lateral displacement from runway centerline, m

-6,000 -8,000 -6,000 -4,000 -2,000 0 2,000 4,000 6,000 8,000 10,000 Distance from brake release, m

DEMONSTRATION AIRCRAFT assuming that the airplane Engine failure was simulated by 2 TAKEOFF GROSS WEIGHT was positioned within 492 ft throttling back the left engine to idle TABLE Zero fuel weight* 100,433 lb (45,556 kg) (150 m) of the valley wall. at 125 kias, the V1 speed for takeoff. The takeoff gross weight for Runway 15 Technical Runway 33 Fuel 15,200 lb (6,895 kg) the technical demonstration Demonstration Test Flight Takeoff weight 115,633 lb (52,450 kg) was calculated based on the airplane empty weight and the The second technical demonstration Zero fuel weight* 100,433 lb (45,556 kg) weight of the crew, passengers, test flight was performed from and fuel on board (table 2). runway 15 (fig. 3). Runway 15 Fuel 13,900 lb (6,305 kg) Table 3 lists the airport con- After liftoff, a right bank was per- Takeoff weight 114,333 lb (51,861 kg) ditions and airplane configu- formed for a 10-deg heading change, ration and takeoff speeds. followed by a left bank for a 60-deg *Includes the weight of three crewmembers, ten passengers, amenities, and potable water. 3 PARO RUNWAY 33 TEST FLIGHT PARAMETERS to perform a 30-deg bank turnback. The available turning radius is based TABLE Airplane configuration on the valley width at the net height Airport conditions Takeoff gross weight: 115,633 lb (52,450 kg) achievable while maintaining not Takeoff time: 03:58 Zulu Takeoff thrust rating: CFM56-7B26 less than 492 ft (150 m) of lateral Landing time: 04:10 Zulu Center of gravity: 18.1%MAC ° separation to the terrain and all ob- Tower-measured temperature: 7 C Stab trim: 5.25 units stacles on either side of the intended Tower QNH: 1,021 mbar = 7,140 ft pressure altitude Flaps 5 takeoff Tower wind: 190 deg at 6 kn track. The limit weight calculations Flaps 15 missed approach and go-around Flaps 40 landing were based on the valley width at Airplane takeoff speeds Air conditioning off; anti-ice off the net height for turnback initiation, V1, 125 kias; VR, 130 kias; V2, 136 kias Left engine pulled to idle at V1

6 AERO Third-Quarter 2003 — July PARO RUNWAY 15 TECHNICAL DEMONSTRATION TEST FLIGHT OVERVIEW 3 6,000 FIGURE Takeoff weight: 114,333 lb (51,861 kg) at 9°C V1, 124 kias; VR, 130 kias; V2, 136 kias Flaps 5 takeoff 4,000 Flaps 15 missed approach, go-around, and landing Air conditioning off; anti-ice off

540 ft 1,200 ft 2,000

1,200 ft 540 ft Runway Runway 15 33 0 Landing Takeoff

-2,000 Brake release Contour heights 540 ft above airport elevation

1,200 ft Lateral displacement from runway centerline, m -4,000

-6,000 -8,000 -6,000 -4,000 -2,000 0 2,000 4,000 6,000 8,000 10,000 Distance from brake release, m

heading change. The left bank took the successfully with a normal flaps 15 However, before the technical airplane across the valley toward the landing using the Druk Air straight-in demonstration flights, Boeing and east wall and avoided a hill that extends landing procedure on runway 15. Druk Air pilots flew practice flights. from the west wall of the valley. The turnback procedure limit After these flights, the pilots deter- A right bank was then held for for runway 15 originally was deter- mined that the critical requirement was an approximate 95-deg heading change, mined to be the turning radius clearing the ridge beyond the village which directed the airplane from the required to perform the 30-deg bank of Silung Nang, which requires a net east side of the valley back toward the turnback. This limit was based on height of 9,100 ft (2.77 km) at the west side and the Silung Nang village. the valley width at the net height turn initiation point. The limit weight The airplane flew over Silung Nang achieved while maintaining a mini- calculations were based on the and the ridge behind it, which required mum 492-ft (150-m) splay outside requirement to achieve this height on an altitude of 9,100 ft (2.77 km). the intended track. the net flight path. The turn radius After the airplane cleared the ridge, a turnback was initiated with a 30-deg 4 PARO RUNWAY 15 TEST FLIGHT PARAMETERS bank while maintaining the designated TABLE V speed. Airplane configuration 2 Airport conditions After completing the turnback Takeoff gross weight: 114,333 lb (51,861 kg) maneuver, the pilots performed a Takeoff time: 04:22 Zulu Takeoff thrust rating: CFM56-7B26 flaps 15 (engine-out landing flap) Landing time: 04:30 Zulu Center of gravity: 18.1%MAC ° missed approach to runway 33, fol- Tower-measured temperature: 9 C Stab trim: 5.25 units lowed by a go-around and a teardrop Tower QNH: 1,020 mbar = 7,140 ft pressure altitude Flaps 5 takeoff Tower wind: 140 deg at 6 kn turnback north of the runway using Flaps 15 missed approach, go-around, and landing the runway 33 turnback procedure. Airplane takeoff speeds Air conditioning off; anti-ice off The condition was completed V1, 124 kias; VR, 130 kias; V2, 136 kias Right engine pulled to idle at V1

Third-Quarter 2003 — July AERO 7 was not limiting at this condition, 3 TECHNICAL DEMONSTRATION verify the capability to match actual assuming a 30-deg bank. TEST FLIGHT ANALYSIS flight profiles. Table 2 shows the airplane takeoff Figures 4 and 5 show the ground gross weight for the runway 15 tech- FDR Analysis tracks and altitude profiles for the nical demonstration flight. Table 4 FDR information was downloaded demonstration test flights from runways lists the airport conditions and airplane 33 and 15, respectively. The calcu- configuration and takeoff speeds. from the airplane after the technical Engine failure was simulated by demonstration test flights. The FDR lated flight paths with one engine throttling back the right engine to idle flight paths were compared with pulled back to idle thrust closely at 124 kias, the V1 speed for takeoff. profiles of predicted performance to match the demonstrated flight paths.

4 PARO RUNWAY 33 TEST FLIGHT GROUND TRACK AND ALTITUDE PROFILE FIGURE

3,000 Data from flight data recorder Predicted data, one engine at idle 940 ft 1,070 ft 1,000 Runway Runway 15 33

-1,000

1,200 ft Chhukha Liftoff Brake 540 ft release -3,000 540 ft Contour heights above airport elevation 1,200 ft Lateral displacement from runway centerline, m -5,000 -12,000 -10,000 -8,000 -6,000 -4,000 -2,000 0 2,000 4,000

Distance from liftoff end, m

9,000

Outbound terrain within 150 m 8,000 Barometric altitude, ft

7,000 -12,000 -10,000 -8,000 -6,000 -4,000 -2,000 0 2,000 4,000 Distance from liftoff end, m

8 AERO Third-Quarter 2003 — July 5 PARO RUNWAY 15 TEST FLIGHT GROUND TRACK AND ALTITUDE PROFILE FIGURE

4,000

Data from flight data recorder Predicted data, one engine at idle

2,000 1,200 ft

540 ft Runway Runway 15 33 0

Brake 540 ft Silung -2,000 release Nang 1,200 ft Contour heights above airport elevation Lateral displacement from runway centerline, m

-4,000 -2,000 0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 Distance from brake release, m

11,000

Outbound terrain within 150 m 9,000 Barometric altitude, ft

7,000 -2,000 0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 Distance from brake release, m

The calculated altitudes at the turnback the turn initiation point. radius available in the valley at each initiation points for both flights were Flying parallel to the valley wall altitude line on a digitized topography within 50 ft (15 m) on the conservative near Silung Nang instead of crossing map. Maximum takeoff weight was calculated by plotting the available side of the predicted altitudes. the ridge removes the requirement to reach 9,100 ft (2.77 km) and allows turn radius and the turn radius required Turn Procedure Optimization a greater takeoff weight. The perfor- as a function of gross takeoff weight. For the technical demonstration test mance then becomes limited by the Figure 6 is an example takeoff flight from runway 15, takeoff weight width of the valley. Through careful weight calculation. The bottom plot was limited by the Druk Air proce- selection of the turn initiation point, shows the airplane altitude at the dural requirement to fly over a ridge additional takeoff weight is possible. turn initiation point. The middle plot after flying south over Silung Nang. The available turn radius as a shows the corresponding airspeeds. To clear the ridge, a net altitude function of altitude was determined The top plot shows the turn diameter of 9,100 ft (2.77 km) is necessary at by computing the maximum turn required for a 30-deg bank, which

Third-Quarter 2003 — July AERO 9 6 PARO TAKEOFF WEIGHT CALCULATION Flaps 5 takeoff FIGURE Air conditioning off; anti-ice off Forward center of gravity No wind Engine failure at V1 12,000 Diameter available at gross height

11,000 Diameter SUMMARY available at ne 10,000 The success of rigorous tech- t height nical demonstration test flights 9,000 at Paro International Airport in Diameter required for 30-deg bank* Bhutan validated the capability of the Boeing 737-700 to 8,000 perform as predicted in a Diameter required for 35-deg bank* 7,000 high-elevation, high-terrain *Assumes a 150-m splay on each side of intended track environment. The test flight data demon- 165 strate that the 737-700 160 ■ Met or exceeded performance ktas 155 expectations for simulated 150 one-engine-inoperative flight maneuvers, proving 145 Airspeed diameter required/available, ft Turn that predicted performance 140 kias is representative of actual 135 performance as recorded 130 by the FDR. ■ Verified procedures for safe 2,000 takeoff and landing opera- 1,900 Gross height tions at Paro, one of the 1,800 world’s most challenging 1,700 airports. 1,600 Net height 1,500 1,400 Druk Air BAe 146 minimum altitude 1,300 1,200 10,800 110,000 112,000 114,000 116,000 118,000 120,000 122,000 Height above airport at turn initiation, ft Gross weight, lb

is solely a function of true airspeed as part of its commitment to ensure and bank angle, and the turn diameter that current and potential customers Editor’s note: available at the corresponding can maximize payload capability Druk Air Royal only net height. during safe takeoff and landing opera- operates BAe 146-100 jets at this Boeing continues to investigate tions in high-elevation, high-terrain time; Boeing is not maximizing the product and operational improvements environments. payload capability of the BAe jets.

10 AERO Third-Quarter 2003 — July IMPORTANCE OF SPEED DURING TAKEOFF TURNBACK PROCEDURES Proper speed is essential when flying takeoff turnback procedures. Lower speeds decrease the climb capability and thereby reduce terrain clearance. Higher speeds increase the turn radius and bring the airplane closer to valley walls. The pilots had the option of overbanking to stick-shaker speed or the initial buffet speed to achieve a smaller turn radius. They also could have combined pitch and roll to trade speed for altitude and reduced turn radius. Although these maneuvers are non-normal and were beyond the scope of this study, the pilots discussed TAKEOFF their potential use to avoid terrain in an emer- gency or in high, unexpected cross-canyon CAPABILITY wind conditions. REFINEMENT Optimal performance was achieved during After the technical demon- the takeoffs from Paro by accelerating the strations, several performance airplane to a speed that was 10 kias faster than options were studied to the minimum safety takeoff speed (10 kias of improve the takeoff weight improved climb). This allowed for 30 deg of bank capability from Paro. These angle and provided the climb gradient necessary included additional optimiza- to initiate the turnback. tion of the turn procedures, increased takeoff thrust, use of alternate forward center of gravity 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 with 114 passengers and 4,850 lb (2,200 kg) of payload. Other enhancements that were stud- ied, such as potential runway extensions and the removal of obstacles surrounding the air- port, will further improve safe operation at Paro.

Third-Quarter 2003 — July AERO 11 INCREASE TAKEOFF GROSS WEIGHT CFM56-7B26/B2, has Takeoff gross weight can be increased been offered to Druk further by using the optimal airplane USING CFM56-7B26/B2 THRUST RATING Air as a new product. takeoff center of gravity (CG) location AND ALTERNATE CENTER OF GRAVITY The CFM56-7B26/B2 instead of the conservative forward-limit thrust rating will location specified by the standard air- The technical flight demonstrations produce at least 2% more thrust than plane flight manual (AFM). The increase were performed using the CFM56-7B26 the CFM56-7B26 rating at the Paro is achieved by using the AFM-alternate thrust rating, which currently is International Airport elevation. The CG takeoff performance option on the highest thrust rating certified on the additional thrust is worth approximately the 737-700, which allows the operator 737-700. A new thrust bump rating, 2,100 lb (953 kg) of additional takeoff to select one of two specified CG gross weight at Paro. locations. Using CG locations aft of the forward limit decreases airplane drag and lowers stalling speeds, thereby increasing takeoff performance. For example, using a 23%MAC CG location instead of the forward-limit location for

12 AERO Third-Quarter 2003 — July runway 15 increases 737-700 takeoff gross weight by 1,200 lb (544 kg). Airport conditions and terrain constraints limited the demonstration takeoff gross weight to approximately 115,000 lb (52,163 kg). However, by optimizing the turn procedures and using the CFM56-7B26/B2 thrust rating and alternate CG performance, takeoff gross weights in excess of approximately 120,000 lb (54,431 kg) are achievable. This improvement would allow Druk Air to fly a 737-700 with a full passenger payload from Paro to all its current initial destinations.

Third-Quarter 2003 — July AERO 13 Miguel Santos is director of international sales for countries in Asia and Africa. During his 24-year career with Boeing, he has held engineering and management positions in advanced engineering, marketing, sales support engineering, marketing management, customer requirements, and sales organizations. Miguel has bachelor’s and master’s degrees in aerospace engineering and an MBA.

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

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

14 AERO Third-Quarter 2003 — July About the Authors

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

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

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 programs during 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 handling qualities of large commercial airplanes and flight deck designs.

Third-Quarter 2003 — July AERO 15