Story ID: 
AINsight: An Eye-opening Lesson on Eye-to-wheel Height
By: Stuart “Kipp” Lau
Caption: Global 5000 accident exposes major safety issues
Word Count: 1990
On Nov. 11, 2007, a Bombardier Global 5000 touched down seven feet short of the runway at Fox Harbour Airport (CFH4) in Nova Scotia. The right main landing gear collapsed before the aircraft departed the runway, struck several grassy berms, and came to a stop 1,000 feet from the initial touchdown point. Two occupants suffered serious injuries and eight others had minor injuries, while the aircraft sustained major structural damage.
A Transportation Safety Board of Canada (TSB) final report identified major safety issues that relate specifically to business aircraft pilots—notably, a lack of available published information on eye-to-wheel height (EWH) and a lack of understanding of the nuances of visual landing systems.
Other issues identified included an operator’s vulnerabilities to mismanaged SMS processes (such as change management, safety risk assessments/management, et cetera) and inadequate safety audits. Airmanship issues, such as appropriate crosswind landing techniques, were also examined.
According to the accident report, the Global 5000 was operated by a privately held charter company based at John C. Munro Hamilton International Airport (CYHM) in Ontario. At the time of the accident, the company operated eight aircraft and one helicopter. The Global 5000 was new to the company and had only 92 hours TT and 26 flight cycles.
The accident airplane departed from CYHM to CFH4 with two pilots and eight passengers onboard. Fox Harbour is a private golf resort with an airport, conference center, and condominiums. First opened in 2001, the airport hosted numerous aircraft ranging from light piston singles to ultra-long-range business jets.
CFH4 has a single 4,885-foot asphalt runway that is 75 feet wide with no electronic navigation aids. However, each runway has a GPS approach, and Runway 33 has an abbreviated precision approach path indicator (APAPI) system installed on the right side.
The Accident
Both pilots had flown into CFH4 on several occasions, operating different aircraft types such as the Beechcraft King Air 350, Gulfstream G100/Astra SPX, and Bombardier Challenger 604. Both pilots were recently type-rated on the Global 5000.
The captain had roughly 9,000 hours TT but had flown only 14 segments in the Global 5000, accumulating approximately 64 hours. While the first officer had 6,400 hours TT, he had logged only nine hours in the Global 5000. The captain, with more experience in the type, was designated as the pilot flying (PF); he also had flown the Global into CFH4 on three occasions before the accident flight.
According to the accident report, the en-route portion of the flight was uneventful. The pilots planned to fly the same approach profile, touching down in the first 500 feet of Runway 33 to maximize the rollout distance available. This plan would require the crew to cross the runway threshold at a lower altitude than the manufacturer’s recommended 50-foot threshold crossing height.
During the approach, the autopilot remained engaged with the aircraft following the FMS-generated vertical path information. According to the analysis, had the crew continued to follow this vertical path, the aircraft would have crossed the threshold at 58 feet and touched down approximately 1,000 feet down the runway. Bombardier performance data indicated that adequate landing distance was available had the aircraft remained on the FMS-generated flight path.
Roughly 1.5 nm from the runway threshold, the PF disconnected the autopilot and transitioned from the FMS vertical flight path guidance to the APAPI guidance, which provided a three-degree path to touchdown approximately 500 feet from the runway threshold.
At approximately 350 feet above the runway elevation, the pilot descended below the APAPI path. Flight data indicated that the pilot further increased his workload by using a wing-low crosswind technique. This cross-controlled condition led to roll spoiler deployment and increasing pilot-induced oscillations as the aircraft neared the threshold.
Two common techniques are used to land large turbojet aircraft in crosswind conditions. The Global 5000 flight manual recommends the “crabbed approach” (wings-level) technique. This is the procedure taught by the manufacturer during simulator training. Pilots flying a crabbed technique apply a drift correction to track the runway centerline and, in the flare, gently apply rudder to align the fuselage with the runway centerline.
The sideslip (wing-low) technique requires a pilot to use a combination of into-wind aileron and opposite rudder to correct the drift and maintain runway centerline. According to Bombardier, this technique increases the risk of pilot-induced oscillations—due to roll spoiler deployment and a swept wing—and can potentially lead to a wingtip strike.
At 0.5 nm from the runway threshold, the PF transitioned completely to runway and ground visual references. The aircraft continued to track below the red/white visual glide path of the APAPI.
Four seconds before impact (0.1 nm from the runway threshold), the auto callout systems announced “50” feet based off the radar altimeter, and the autothrottle system changed from SPEED to RETARD and the thrust levers automatically moved to the IDLE position. From this point on, according to the report, the airspeed continued to decrease, placing the aircraft into a precarious low-energy state. Without the addition of thrust, any corrections to the flight path would be ineffective.
The aircraft touched down hard and short of the runway. In the accident sequence, the right main landing gear collapsed and the aircraft departed the runway, striking several mounds, before coming to rest 200 feet short of a condominium. Extensive damage to the aircraft’s landing gear, wing structure, flaps, fuselage, and engines was attributed to the hard landing and off-runway excursion.
“Because the crewmembers were flying the same approach profile they had used many times before at CFH4, at no point on the approach did they recognize that they were on an unsafe flight path,” the report says. Throughout the approach, there were no callouts by the pilot monitoring (PM) for any corrections, since all seemed to be going according to plan—or at least no different than the view out the windshield of the smaller Challenger 604, which both pilots had previously flown into the airport.
“Although consideration had been given to the aircraft’s larger size in regard to ground maneuvering,” the report says, “no consideration had been given to the Global 5000’s greater eye-to-wheel height (EWH) and the implications of the larger aircraft flying the accustomed flight profile at CFH4.”
What Is Eye-to-wheel Height?
EWH is the vertical distance from the pilot’s eyes to the lowest portion of the aircraft in the landing attitude. According to the TSB, “Knowledge of an aircraft’s EWH is necessary for flight crews to assess the adequacy of a visual glide slope indicator (VGSI) system for the aircraft flown.”
EWH varies by aircraft type. A light business jet may have an EWH of less than four feet, whereas a Boeing 747 has an EWH of 45 feet.
As part of the investigation, the TSB interviewed several airline transport-rated pilots to determine their awareness and knowledge of EWH and VGSI limitations. This group included instructors, check pilots, chief pilots, inspectors, and test pilots. In general, it was determined that pilots are not aware of the definition of EWH or the EWH that relates to the aircraft they fly. Likewise, most pilots did not understand the nuances of the different classifications of PAPI systems.
Investigators also found that EWH information was not available—nor was it required to be by regulation—in most business aircraft flight manuals. Likewise, this topic was not covered in type-specific ground school or simulator training.
For comparison, EWH information was calculated for the Global 5000 and Challenger 604 aircraft at various weights on a three-degree glide path. The Global 5000 EWH ranged from 16.35 to 17.20 feet, whereas the Challenger 604 has an EHW of 12.11 to 12.18 feet—a significant difference of up to five feet. This is noteworthy given that the accident aircraft was operated below both the FMS-generated and APAPI glide paths.
VGSI/PAPI Systems
In general, aviation regulatory agencies in both Canada and the U.S. employ different types of PAPI systems to provide the minimum wheel clearance over the threshold for the most demanding aircraft using the runway on a regular basis. Keep in mind, this may not be the largest aircraft using that airport. As such, PAPI systems are based on the EWH of the common aircraft that the airport is intended to serve.
For operators of large aircraft flying into small airports, it is important to know the EWH of your aircraft and the type of VGSI/PAPI installed. “Knowledge of aircraft EWH is necessary to assess whether a VGSI system is appropriate for the aircraft type being flown,” the TSB notes.
In the case of the Global 5000 with an EHW of 16 to 17 feet, the APAPI was only appropriate for aircraft with an EWH of 10 feet, which compromised the touchdown crossing height (TCH).
In Canada, the Canada Air Pilot general pages describe the different types of PAPI systems available. Canada Flight Supplement Information documents will detail the specific type of PAPI systems installed at each airport.
In Canada, the following types of PAPI systems are available:
APAPI. Abbreviated PAPI for aircraft with eye-to-wheel height up to 10 feet.
PAPI 1. PAPI for aircraft with eye-to-wheel height up to 10 feet.
PAPI 2. PAPI for aircraft with eye-to-wheel height up to 25 feet.
PAPI 3. PAPI for aircraft with eye-to-wheel height up to 45 feet.
In the U.S., the FAA Order JO 6850.2B classifies PAPI systems by “height groups,” providing appropriate eye-to-wheel height and visual threshold crossing height information. The FAA provides airport-specific information for PAPI systems digitally through the Airport Facility Directory.
In the U.S., the following types of PAPI systems are available:
Height Group 1 (P1). PAPI for aircraft with eye-to-wheel height of 10 feet or less with a visual threshold crossing height of 40 feet (+5/-20 feet). This group is appropriate for general aviation, small regional airliners, and smaller business jets.
Height Group 2 (P2). PAPI for aircraft with eye-to-wheel height of 15 feet with a visual threshold crossing height of 45 feet (+5/-20 feet). This group is appropriate for larger turboprops, smaller single-aisle airliners (Boeing 717/737, Embraer E-jets, Bombardier CRJs, et cetera), and large-cabin business jets (Challenger 604, Gulfstream G450, et cetera).
Height Group 3 (P3). PAPI for aircraft with eye-to-wheel height of 20 feet with a visual threshold crossing height of 50 feet (+5/-15 feet). This group is appropriate for larger single-aisle airliners (Airbus A320/321, Boeing 757) and ultra-long-range business jets (Gulfstream G650, Global 5000).
Height Group 4 (P4). PAPI for aircraft with eye-to-wheel height of more than 25 feet with a visual threshold crossing height of 75 feet (+5/-15 feet). This group is appropriate for widebody airliners (Airbus A300/330/340/350/380 and Boeing 747/767/777/787).
In its report, the TSB concluded that, among many items, “the flight crewmembers flew the approach profile as they had done in the past on the smaller Bombardier Challenger 604, with no consideration for the Global 5000’s greater EWH, resulting in a reduced threshold crossing height.”
Furthermore, “The APAPI guidance, although not appropriate for this aircraft type, would have assured a reduced main landing gear clearance of eight feet above the threshold.” The PF descended below the APAPI guidance, further reducing the TCH.
This Canada TSB accident report is instructive for any operator flying larger aircraft into smaller airports, regardless of location. I only scratched the surface of what’s in the final report, so I’d highly recommend you also read that document, which goes into detail on the safety management system process, as well as inadequate safety audits by third parties. As an example, one audit essentially “rubber stamped” that it was okay for the operator to fly the Global 5000 into CFH4 without any additional mitigations. This proved to be untrue.
The opinions expressed in this column are those of the author and are not necessarily endorsed by AIN Media Group.