H25B / AS29, en-route / manoeuvring, near Smith NV USA, 2006
H25B / AS29, en-route / manoeuvring, near Smith NV USA, 2006
On 28 August 2006, a Hawker 800 collided with a glider at 16,000 feet in Class 'E' airspace. The glider became uncontrollable and its pilot evacuated by parachute. The Hawker was structurally damaged and one engine stopped but it was recovered to a nearby airport. The Investigation noted that the collision had occurred in an area well known for glider activity in which transport aircraft frequently avoided glider collisions using ATC traffic information or by following TCAS RAs. The glider was being flown by a visitor to the area with its transponder intentionally switched off to conserve battery power.
On 28 August 2006, a Raytheon Hawker 800 XP (N879QS) being operated by Net Jets Aviation on an "executive/corporate" flight from Carlsbad CA to Reno NV was in collision in day VMC with a manoeuvring glider whilst en route at 16,000 feet in Class 'E' airspace. Both aircraft sustained substantial damage. The glider became uncontrollable and the pilot, the only occupant, evacuated by parachute. The Hawker was diverted to the nearest suitable airport, Carson City, where it was landed with the gear retracted after the crew had been unable to select it down. Minor injuries were sustained by both Hawker pilots as a result of the impact and by the glider pilot during his parachute landing. The three passengers on board the Hawker were uninjured.
An Investigation was carried out by the NTSB. The jet aircraft involved was fitted with a 30 minute CVR from which data up to the point of collision were successfully downloaded but it was not fitted - and was not required to be fitted - with an FDR. Both aircraft were fitted with a transponder but the equipment in the glider was switched off. The effect of this was that the glider was not visible to ATC or to the serviceable TCAS ll equipment fitted to the jet aircraft. The in-flight visibility and disposition of cloud was such that neither represented any impediment to 'see and avoid'.
The 38 year-old Hawker aircraft commander who was PF at the time of the collision, had 6,134 hours total flying time which included 1,564 hours on type. The 35 year old First Officer had 3,848 hours total flying time which included 548 hours on type. Both pilots were wearing sunglasses at the time of the event, the First Officer in the form of sunshades clipped over required corrective glasses. The 57 year-old glider pilot had 455 hours total flying time including 3 hours on type and held a PPL with glider rating and with a valid Japanese Class 2 Medical Certificate. He did not hold, nor was he required to hold, a current FAA-issued Medical Certificate.
It was established that the Hawker had been on a steady heading and tracking northwest towards Reno for several miles. It had been cleared to descend from 16,000 feet to 11,000 feet and had just been transferred to Reno TRACON when the collision occurred. The glider had been in a spiralling left hand climbing turn with a 30° AoB. Although both Hawker pilots stated that they had been "looking out the window before the collision", the Captain of the Hawker and the glider pilot both reported having seen the other aircraft for not more than a second before the collision which made effective avoidance action impossible. The Captain stated that she had only seen the glider "a moment before it filled the windshield". On sighting "something out of the corner of her eye to the left", the Captain looked that way and saw "a glider filling the windshield" and "moved the control yoke down and to the right" in an attempt to avoid hitting it. The First Officer did not see the glider at all and remained unaware of the cause of what he described as an "explosion" of the Captain's side of the instrument panel. Both pilots stated that after the collision the flight deck had become noisy due to external air ingress. The Captain's headset had been knocked off but she was able to recover control of the aircraft. The First Officer, as yet unaware of the cause of the obvious structural damage, advised ATC that the aircraft had "some sort of structural problem and declared an emergency", requesting radar vectors to the airport because of severe instrument panel damage. As the aircraft continued north, the crew saw an airport at their 11 o'clock at 20 nm and after ATC confirmation that this was Carson City, they decided to divert there. They then "noted that the right engine had shut down as a result of the impact" and, after finding that the landing gear would not extend normally, eventually made a gear up landing on runway 27 centreline and came to a stop uneventfully. The aircraft was equipped with a functioning transponder and TCAS ll but no TA or RA was generated in relation to the proximity of the glider.
The glider pilot stated that after an earlier flight review in a different type of glider, he had made his first one hour flight in the accident glider type and then taken off from Minden in it on a second flight approximately two hours prior to the collision. He had planned to conduct thermal flying for about five hours and initially "wanted to stay in the local area in order to familiarise himself with the accident glider". Whilst undertaking this familiarisation, he was climbing in a thermal in a 30° left banked spiral turn at 50 KIAS when he "saw a jet aircraft heading toward him". He reported that he may have made a slight nose down control input but with only a second available, collided with the Hawker which hit the glider's right wing in the vicinity of the joint between the outboard and inboard wing sections. The glider had subsequently entered a flat spin so he had removed the canopy and bailed out with his parachute then opening normally. He had seen the glider spiral to the ground below him and had noted that the left wing and the inboard section of the right wing had remained attached to the fuselage. He sustained minor injuries when his parachute dragged him along the ground after landing and, after waiting near the landing area for 1½ hours, he had begun walking along a track towards Carson Valley from where, after just over two hours walking, he was picked up. He explained that as a visitor to the area, he had not been renting a glider from one of the three main glider groups in the area but was instead borrowing the glider from a friend. As a result of this, he had not had the benefit of an airspace risk briefing which would have been provided to any visitor taking a group glider for a solo flight and he stated that he had been unaware of the jet aircraft routes into and out of Reno. The glider was equipped with a GPS unit and a Mode C transponder but neither were turned on. The pilot stated that "he did not turn on the transponder because he was only intending on remaining in the local glider area and because he wanted to reserve his batteries for radio use". It was noted that the glider had both a main and a spare battery but due to its previous flights, "the pilot was unsure of the remaining charge in the battery". The glider was fitted with a radio but the pilot was not in radio contact with Reno TRACON nor was he required to be.
It was noted that in the area where the collision occurred, soaring regularly occurs up to the limit of Class 'E' airspace above which Class 'C' airspace is designated and a functioning Mode C transponder is required unless a special glider operations box is implemented which it was reported usually occurs during mountain wave conditions.
Impact damage to the Hawker was noted to have included:
- to the nose structure with a section of the glider wing spar remaining embedded in it
- a breach of the forward pressure bulkhead
- destruction of the Captain's instrument panel such that the primary instrumentation was no longer useable
- loss of elevator control forward of a neutral position
- leading edge damage to the right wing which had compromised its fuel tank.
- leading edge damage to the horizontal stabiliser including a large hole that extended aft to the mounting flange
- fan blade damage to the left engine and to its lower cowling drain mast
- damage to the right engine fan blades and significant damage to the inlet area which left a large hole in the cowling.
- fibreglass embedded in the right engine tail pipe with fuel dripping from the lower cowling and fuel control unit.
In addition, superficial damage to the underside of the fuselage and inboard wings had been caused by landing with the gear retracted.
Interviews with the Hawker passengers found that when they had been instructed by the flight crew to tighten their belts for the wheels up landing which followed the collision, one passenger had found that their seat belt attachment had failed and that the same had occurred again after moving seats. Examination of the aircraft disclosed that the attachments concerned were faulty and a sequence of rectification actions ensued. Eleven days after the accident, NetsJets implemented a fleet inspection to validate the integrity of these attachments, and this was then followed by a similar Raytheon instruction to all operators and in February 2007, a MSB requiring modification of the lap belt attachment shackles and the introduction of a mandatory "check of seat belt attachment hook and safety clip for distortion and security" as part of the 300 hour inspection requirement.
The Investigation focused on three main areas of interest in relation to the collision:
- The overall management of the glider/transport aircraft collision risk in the area south of Reno
There existed a previous (1997) Safety Recommendation on Reno Area Airspace and radar coverage made by the FAA Reno Flight Standards District Office to the FAA Office of Accident Investigation which "offered a number of solutions" to what was described as "an extreme aviation safety concern" in respect of the risk of collisions between gliders and transport aircraft approaching and departing from Reno. None of the four solutions offered had been implemented by the FAA. Since then, it was noted that glider/jet aircraft NMACs had continued to occur despite considerable efforts (with some success) by the Reno TRACON facility to engage with and educate the glider community. During the Investigation, Reno TRACON personnel indicated that TCAS RA annunciations due to transponder-equipped gliders are not uncommon for arriving and departing Reno air traffic with many causing deviations from ATC Clearances. TCAS RA data are only retained for 30 days and details of four in that period, all involving aircraft operating under 14 CFR Part 121, were provided. It was stated that display of VFR transponder codes and reports from transport category aircraft that gliders are operating within the final approach course for Reno are routinely "numerous" and that "controllers can sometimes see primary radar returns from a suspected glider, but are not able to ascertain its altitude and if it is a glider".
- The effectiveness of 'see and avoid' as a collision avoidance technique
Although it was noted that the applicable regulations require all pilots (including those operating IFR) to maintain sufficient vigilance to be able to see and avoid other aircraft when visibility permits, it was considered that various factors could diminish the effectiveness of the see-and-avoid principle, some of which were evident in this accident. These included "the high closure rate of the Hawker as it approached the glider" and "the slim design of the glider" which would have made it difficult for the Hawker crew to see it. However, the lack of any radar data for the accident glider's flight meant that it was "not possible to determine at which points each aircraft may have been within the other's available field of view". The Investigation noted the ATSB Report on this subject which acknowledged that whilst the see-and-avoid principle "undoubtedly prevented many collisions, the concept was a flawed and unreliable method of collision avoidance (and) usually failed to avert collisions at higher speeds". The data available to that Study estimated that see-and-avoid prevents only 47% of collisions when the closing speed is greater than 400 knots. The ATSB concluded in its report that "because of its many limitations, the see-and-avoid concept should not be expected to fulfil a significant role in future air traffic systems". It was also noted that having recognised the limitations of the see-and-avoid concept, the FAA "has turned to other methods such as TCAS to ensure traffic separation”.
- The importance of transponder use as a means to avoid collisions between high speed powered aircraft and gliders
It was noted that whilst the regulations applicable to gliders do not require them to have a Mode C transponder installed, they do say that any aircraft fitted with a serviceable transponder must operate in Mode C if so capable. Whilst not quoting the latter regulation, all three local gliding centres had briefing material which stressed that soaring was likely to occur in the Class 'E' airspace also used by jet transport aircraft inbound to/outbound from Reno and variously stressed the importance of carrying and using Mode C transponders as a means to collision avoidance.
The Investigation determined that the Probable Cause of the accident was "the failure of the glider pilot to utilise his transponder and the high closure rate of the two aircraft, which limited each pilot's opportunity to see and avoid the other aircraft".
The Final Report was adopted by the NTSB on 20 March 2008 but was not published until 21 May 2013. No Safety Recommendations were made.
- Mid-Air Collision
- Loss of Separation
- Operation without a Transponder or with a Dysfunctional Transponder
- Airborne Collision Avoidance System (ACAS)
- See and Avoid
- Limitation of the See-and-Avoid Principle, Alan Hobbs, ATSB (Australia), Nov 2004.
- IFR / VFR – Air Traffic in Airspace E, Sympathetic Cooperation, by BFU, December 2011