Photo: Aircraft Damage, from Transportation Safety Board of Canada, Aviation Investigation Report, Photo 4.

Eddie Sez:

This is a classic mishap where aiming for Brick One leads to bad results. Ever since one of my Air Force Boeing 747 squadron mates put eighteen wheel prints in the overrun at Andrews, the math behind aircraft deck angle has been a priority for me. What the Canada Transportation Safety Board calls "Eye-to-wheel height" really misses the point. What pilots really need to understand is how far behind their aim point the wheels will contact the runway. The geometry of the aircraft on approach fundamentally changes the point at which the wheels will touch in relation to the pilot's aim point. The pilots were experienced in the Challenger 604, which has an abnormally flat deck angle on approach. In that airplane, they were able to successfully aim for 500 feet down the runway and land fairly close to that target. In an airplane with a higher deck angle, such as the incident's BD-700, this is not possible.

In this model of BD-700 the main gear are 41 feet behind the pilots, but the wheels will touch 285' behind the pilot's aim point if the pilot does not flare. Hard to believe? See Flight Lessons / Deck Angle for the math.

What follows are quotes from the sources listed below, as well as my comments in blue.


Accident Report


Narrative

[Transportation Safety Board of Canada, Aviation Investigation Report A07A0134, §1.1]


Analysis

Photo: Aircraft eye-to-wheel height, from Transportation Safety Board of Canada, Aviation Investigation Report A07A0134, photo 5.

[Transportation Safety Board of Canada, Aviation Investigation Report A07A0134, §1.1]

  • The captain was certified and qualified for the flight in accordance with existing regulations. At the time of the accident, he had accumulated 9188 hours of total flying time, including 3196 hours on turbojets. In his previous employment, he had accumulated over 2500 hours as captain on a DHC-6 Twin Otter, over 1000 hours on a Beechcraft B200 and over 1000 hours as captain on a Westwind WW24 turbojet. Since joining Jetport Inc. (Jetport) on 24 July 2000, he had accumulated 2196 hours as captain on the Gulfstream G100 and Bombardier Challenger 604 (CL604).

  • Before the occurrence flight, the captain had a total of 64 hours on the Global 5000, all flown on the occurrence aircraft (C-GXPR). The captain had flown other Jetport aircraft, including the CL604, into CFH4 approximately 75 times in the previous years. However, this was only his third landing in CFH4 at the controls of the Global 5000.
  • The mishap aircraft was the longest aircraft the captain had ever flown, it is unlikely he would have ever been taught about the distance between his aim point and wheel no-flare distance. His most formative jet experience was in the Challenger 604, which has an unusual landing geometry.

  • The captain's first landing at CFH4 with the Global 5000 was on 21 October 2007, accompanied by the support pilot. The aircraft landing weight for that flight was 63,032 pounds, approximately 2,000 pounds heavier than on the occurrence flight. The ceiling and visibility were good and the winds were from the west at 13 knots gusting to 20 knots. The turbulent approach was flown manually from an altitude of 1200 feet asl and with the autothrottle engaged. The captain planned to touch down in the first 500 feet of runway, as he normally did in CFH4. The captain had just initiated the flare when the aircraft touched down, approximately 200 feet past the threshold, closer to the threshold than planned. This was debriefed by the support pilot.

  • The first officer was certified and qualified for the flight in accordance with existing regulations. At the time of the accident, he had accumulated 6426 hours of total flying time. In his previous employment, he had accumulated over 2000 hours of flying light and heavy turboprop aircraft. Since joining Jetport in 2000, he had accumulated 3064 hours, of which 2540 hours were as captain, on the Gulfstream G100 and the CL604 turbojets.

  • In July 2007, he completed the Global 5000 ground school and level D simulator training at the Bombardier Aerospace Training Centre in Saint-Laurent. On 03 August 2007, the first officer completed a CARs subpart 704 initial PPC monitored by a Transport Canada inspector. During training, the first officer accumulated 34 hours of level D simulator time.

[Transportation Safety Board of Canada, Aviation Investigation Report A07A0134, §1.9.4] C-GXPR's EWH calculations were completed using the actual conditions, an aerodrome at sea level, a 3.0° flight path and the landing gear fully extended. For the occurrence flight, the EWH was determined to be 16.35 feet. Based on the Global 5000 maximum landing weight of 78,600 pounds, the greatest EWH for the Global 5000 in the approach configuration was determined to be 17.2 feet.

[Transportation Safety Board of Canada, Aviation Investigation Report A07A0134, §1.9.5] Calculations were also completed by the manufacturer to obtain the EWH of the Bombardier Challenger 604 (CL604), assuming a 3.0° flight path, in both the light landing configuration and the heavy landing configuration. The EWH in the light landing configuration was calculated using a landing weight of 28,000 pounds and was determined to be 12.11 feet

The difference in eye-to-wheel height of the two airplanes is a mere 5 feet. That might explain the difference between just barely clearing the runway's edge and hitting the runway's edge in this particular case, but it doesn't explain the reason the pilot's 500 feet aim point is inappropriate. We can do better. . .

Figure: BD-700 deck angle, from Eddie's notes.

The investigators failed to consider the distance between the pilot's aim point and the theoretical point the wheels would touchdown without a flare, based on that aim point. Because of the aircraft's positive deck angle and the height of the pilot's eyes above the wheels, the distance is not one-for-one. Few manufacturers publish their aircraft deck angles but it can be estimated. In the case of the BD-700, using a photo of the aircraft on approach in the accident report we can determine the BD-700 has an approach deck angle of 5°, which is typical of most passenger jets. (The pilots were most recently qualified on a Challenger 604, which is a notable exception to this average. The 604 has an approach angle which appears to be very close to zero.)

Figure: BD-700 deck angle, from Eddie's notes.

If a BD-700 pilot flies an on-speed 3° glide path toward an aim point on a runway and does not flare, the aircraft's wheels will touch the runway 285 feet behind that aim point. In the case of this mishap, the pilot was on track to do just that, but when the throttles went into the retard mode the aircraft was not over the runway and the pilot's pitch feel would have been different because there was less ground effect. The pilot failed to compensate and the airplane dipped below the glide slope he had set up.

The lesson should be clear: your wheels will touch far behind your aim point unless you flare consistently. You will be hard pressed to do that unless your airplane is over the runway when you flare. Aiming short of a normal 750' to 1,000' aim point removes all margin for error.

More about this: Technical / Aim Point versus Touchdown Point.


Probable Cause

Figure: Aircraft Damage, from Transportation Safety Board of Canada, Aviation Investigation Report, Photo 7.

[Transportation Safety Board of Canada, Aviation Investigation Report A07A0134, §3.1]

  1. The crew planned a touchdown point within the first 500 feet of the runway to maximize the available roll-out. This required crossing the threshold at a height lower than the manufacturer's recommended threshold crossing height (TCH).
  2. The flight crew members flew the approach profile as they had done in the past on the smaller Bombardier Challenger 604 (CL604), with no consideration for the Global 5000 greater aircraft eye-to-wheel height (EWH), resulting in a reduced TCH.

  3. The abbreviated precision approach path indicator (APAPI) guidance, although not appropriate for this aircraft type, would have assured a reduced main landing gear clearance of eight feet above threshold. At 0.5 nm, the pilot flying (PF) descended below the APAPI guidance, further reducing the TCH.

  4. The pilot used the wing-low crosswind technique, increasing his workload and resulting in pilot-induced oscillations.

  5. Both pilots' low experience on the Global 5000, combined with the PF's high workload, affected their ability to recognize the unsafe approach path and take appropriate corrective action.

  6. With the aircraft in a low energy state, the pitch up to 10.6º without an associated thrust increase could not correct the flight profile, resulting in the impact with the sloped surface before the runway threshold.

  7. The impact with the sloped surface initiated a sequence resulting in the collapse of the right main gear, a loss of directional control, the eventual departure from the runway surface, substantial damage to the aircraft, and some injuries.

  8. Contrary to the manufacturer's recommended practices, Jetport's standard operating procedures (SOPs) sanctioned descent under electronic or visual glide slope guidance, with a view to extending the landing distance available as acceptable and good airmanship; this contributed to the aircraft landing short of the runway.

  9. The lack of an effective transition from traditional safety management to a functional safety management system (SMS) as required by Jetport's private operator certificate (POC) prevented an adequate risk assessment of the introduction of the Global 5000 into its operations and contributed to the accident.

  10. An inappropriate balance of responsibilities for oversight between the regulator, its delegated agency, and the operator resulted in Jetport's inadequate risk assessment not being identified.

  11. C-GXPR's EWH calculations were completed using the actual conditions, an aerodrome at sea level, a 3.0° flight path and the landing gear fully extended. For the occurrence flight, the EWH was determined to be 16.35 feet. Based on the Global 5000 maximum landing weight of 78,600 pounds, the greatest EWH for the Global 5000 in the approach configuration was determined to be 17.2 feet.

  12. Calculations were also completed by the manufacturer to obtain the EWH of the Bombardier Challenger 604 (CL604), assuming a 3.0° flight path, in both the light landing configuration and the heavy landing configuration. The EWH in the light landing configuration was calculated using a landing weight of 28 000 pounds and was determined to be 12.11 feet

See Also:


References

Transportation Safety Board of Canada, Aviation Investigation Report A07A0134, Touchdown Short of Runway, Jetport In., Bombardier BD-700-1A11 (Global 5000) C-GXPR, Fox Harbour Aerodrome, Nova Scotia, 11 November 2007