Very large trial!

Boschen had originally proposed the DC-10 concept to the Victorian government in 2008 as an unsolicited proposal, and following the February 2009 fires, tendered for and won the VLAT trial contract last November. “We had looked at a range of medium to large tanker operators, but 10-Tanker appeared to be the most advanced with their concept,” Boschen told us. “We got the DC-10 placed on our Australian AOC with some great cooperation from CASA – their Air Transport Operations Group (ATOG) office in Brisbane was excellent to deal with, and they found the concept very interesting. The aircraft is operated in the same manner as it is in the US and follows FAA maintenance and flight crew training proficiency regulations.”

10-tanker

10-Tanker Air Carrier is division of US-based Omni Air International which was originally founded as a freight airline in 1983 before moving into passenger operations in 1995. Today, Omni operates a fleet of DC-10, 757 and 767 airliners out of Victorville in southern California, mainly on charter work on behalf of the US Department of Defense as well as for various package holiday and cruise operators.

10-Tanker’s Chief Supervisor, Jack Maxey, who lead the Avalon trial, says the DC-10 was a natural choice for the company when it began developing the tanker concept, as the airframe is considered over-engineered and rugged, it had the necessary ground clearance for the external tanks, there were plenty of sound airframes and spares available, and the company already had experience operating the type.

The company currently has two DC-10 tankers, 910 and 911, and plans to convert more. The 2010 northern fire season will be 10-Tanker’s fifth season operating the DC-10. In total, the two tankers have fought in 50 fires and have carried out more than 340 water or retardant drops against active fires, as well as another 200 test and demonstration drops. The 2009 season was one of the company’s busiest, with 130 hours flown against fires, and on one day last year, nine missions being flown in one day from Victorville against fires in the Los Angeles area.

“On the ground, the aircraft can have its retardant tanks refilled and be turned around within 18 to 20 minutes if we’re operating close to the fire and don’t require refuelling,” Maxey said. “We usually need about 30 minutes for the first call out of the day, and we’ve been operating here in Victoria on a 30 minute standby for the trial.”

For the Australian deployment of the DC-10, 10-Tanker brought a crew of seven to Avalon, three pilots, two flight engineers and two mechanics, as well as a spotter aircraft pilot. On a typical mission, the aircraft will fly with two pilots and a flight engineer.

911

The Victorian trial aircraft, call sign ‘Tanker 911’, was a former Continental Airlines and Omni Air passenger DC-10-30 before being converted to tanker configuration in 2008. It is powered by three GE CF6-50C engines, each providing 51,000lbs of thrust (226.9kN).

The aircraft is fitted with three large tanks mounted longitudinally on its underside capable of carrying up to 45,000 litres of water, or 42,000 litres of retardant or water injected with foam concentrate. The tanks are the same as those used on Erickson S-64 Air Cranes that have become common sights in NSW and Victorian skies in recent fire seasons, albeit with the centre tank widened and an aerodynamic bow and stern added, and the tanks’ hydraulics and electronics relocated to the DC-10’s cargo hold forward of the wing.

“We used Erickson’s tanks as they were off the shelf, were a nice fit for the DC-10, and there was no reason to re-invent the wheel,” Maxey told us. “The only changes we made were a bit of streamlining and we widened the centre tank.”

Interestingly, apart from having its heavy passenger cabin interior and underfloor cargo handling system completely stripped out, the aircraft’s centre fuselage landing gear strut was also dispensed with. The longer-ranging DC-10-30 was fitted with the centre gear assembly in order to better spread the heavier aircraft’s weight on airport ramps. But because in tanker form the aircraft will never come close to the former airliner’s maximum take off weights (MTOW), deleting the centre strut and fairing over the gear bay not only allowed for the fitting of the underside water/retardant tanks, but saved several thousand kilograms in the process. Indeed, all the modifications to the DC-10 resulted in more than 60 tonnes being removed from the empty weight of the aircraft.

Apart from the external tanks and the associated hydraulic and electrical systems, other modifications to the DC-10 included the addition of several reinforcing bulkheads in the cargo hold ahead and behind the wing box to provide additional structural support for the external tanks, and load drop controls and an enhanced communications suite in the flight deck.

Maxey told us that the DC-10 tanker had never exceeded a MTOW of 173,000kg (380,000lbs), well below the DC-10-30’s certified MTOW of 259,000kg (572,000lbs). Therefore, sea-level take offs are usually performed at de-rated thrust levels giving increased engine longevity, and although most missions are short in duration resulting in a higher than usual number of cycles, these are performed at light weights.

“The external tanks have given us an eight per cent increase in fuel burn, and there is more wind noise noticeable,” Maxey explained. “We also trim the nose up a little when operating with full tanks, and then as we drop we run the trim back to cancel out the slight shift in CG.”
The aircraft has an operating radius of about 740km when fully loaded, bringing all of Victoria, the ACT and southern NSW up to Sydney, across to Adelaide, and all of Tasmania in range from its Avalon base.

Conops

Accompanying the DC-10 to Australia was a King Air E90, also owned by 10-Tanker but operated by a pilot employed by Dyncorp and contracted to CALFIRE, the Californian Department of Forestry and Fire Protection.

Pilot Bob Justo-Coward is a former ground fire fighter and smoke jumper aircraft pilot, but now flies the King Air alongside other aircraft such as OV-10s, O-2As as spotter aircraft in support of VLAT operations.

“I can be in the air within 20 minutes and will fly out ahead of the large tankers and coordinate with the incident commander on the ground,” Justo-Coward told us. “He’ll tell me where he wants the tankers to drop, and will help me clear any conflicting air traffic from our area.”

Once the VLAT has arrived, the spotter aircraft will lay down a ‘show me’ smoke trail by dumping oil into his aircraft’s exhaust to show the tanker where he wants the drop to be while the tanker is observes from about 2000 feet. The spotter aircraft will then turn and climb to join up with the tanker at about 800 feet at the end of the downwind leg, before taking the lead as they turn onto base. As the aircraft join up, the spotter pilot will confirm with the tanker crew the various deconfliction and other safety procedures.

The run to the fire is usually planned so the DC-10’s speed is 150 knots and the load can be dropped from around 200 feet above the fuel source, thus allowing the water or retardant to have slowed sufficiently to fall vertically onto the fuel source. If over scrubby country, this could be little more than 200 feet above the ground, but may be as much as 400 feet or more if flying above tall trees. If a load is dropped too low, it may hit the fuel source at an angle and thus create dry ‘shadows’ on trees or steep slopes. And if dropped from too high, the load may partially evaporate or be dispersed by winds before it hits the target.

On approach to the drop, the spotter will typically be between 400 and 800 metres ahead of the tanker, will be calling out terrain height variations if required, and will confirm that the taker’s approach and speed are stable and wings are level before committing to the drop.

By this time, the tanker crew will have been told the coverage required on the ground by the spotter pilot, and the flight engineer will have set the drop switched to the appropriate level. The controls will allow the tanker to drop anywhere between 18 and 45 litres of water or retardant per square metre, resulting in a drop roughly between 600 metres and 1.2km long if the entire load is released in one pass.

At the drop zone, the spotter will lay down another smoke trial along the axis he wants the tanker to follow, and will point out nearby landmarks such as a ridge line, rock outcrop or tall tree in case the smoke trail disperses. “You’ve got to watch carefully which way the smoke drifts and make small adjustments accordingly,” said Maxley. “Big fires make their own weather and the winds can be unpredictable, and the spotter might have to tell you to adjust left or right by a wingspan as he comes off his run.”

On the tanker pilot’s command, usually as they fly into the spotter plane’s smoke trial or a landmark passes under the nose, the flight engineer will press and holds down a large button on the centre console between the pilots to release the load. Emergency dump buttons are provided for both pilots on both of the DC-10’s control column as a backup.

Occasionally a tanker will be required to make two or more passes with a single load, sometimes using the terrain to its best advantage or perhaps laying down a corner of retardant ahead of a fire front. But more commonly, a VLT’s load will be used to either create or bolster a fire break ahead of an advancing front using a single drop of fire retardant, while smaller aircraft and helicopters can be used simultaneously to attack spot fires and the fire front itself.

In large fires with multiple medium and large tankers operating such as those seen in California last year, a spotter plane may stay on station for up to four hours and coordinate multiple tanker drops. In such a scenario, the spotter will fly an almost continuous race-track pattern, alternatively flying ‘show me’ and then drop leads on each pass.

Next Year?

The DC-10 VLAT trial was being closely monitored by the Bushfire Cooperative Research Centre (BushfireCRC); an organisation representing multiple bodies including state fire authorities, the Bureau of Meteorology, universities, forestry companies and bodies, and emergency services organisations; and a report by BushfireCRC on the success of the three month trial was expected to be handed to the Victorian government in May.

To this end, BushfireCRC personnel have observed research drops as part of their assessment, and have liaised extensively with its various representing bodies on the overall success of the trial. A decision on whether to deploy the DC-10 or a similar capability in future fire seasons will also take into account forecast weather patterns and risk assessments.