Tag: air tanker

The Federal Aviation Administration has issued new rules aimed at reducing the crashes of aircraft caused by “widespread fatigue damage” on older airplanes. As part of the justification for the new policy they gave 12 examples where fatigue cracks and other failures of metal parts were found on aircraft. None of them resulted in crashes or fatalities except for three that involved air tankers.

The new directive affects some turbine powered transport aircraft with a maximum takeoff weight greater than 75,000 pounds with a type certificate issued after January 1, 1958. It apparently does not apply to air tankers and only affects aircraft operated under Parts 121 or 129, scheduled air carriers and foreign air carriers.

The new rule requires:

1. Establish a limit of validity of the engineering data that supports the structural maintenance program (LOV);

2. Demonstrate that widespread fatigue damage (WFD) will not occur in the airplane prior to reaching the LOV; and

3. Establish or revise the Airworthiness Limitations section in the Instructions for Continued Airworthiness to include the LOV.

Here are the three air tanker crashes cited in the report:

• Lockheed C-130A: Fatigue cracks in the wing structure. On August 13, 1994, while responding to a forest fire in the Tahachapi Mountains near Pearblossom, California, the airplane experienced an in-flight separation of the right wing. All 3 flight crewmembers were killed, and the airplane was completely destroyed.

• Lockheed C-130A: Fatigue cracks in the wing structure. On June 17, 2002, while executing a fire retardant drop over a forest fire near Walker, California, the airplane’s wings folded upward at the center wing-to-fuselage attachment point, and the airplane broke apart. All three flight crewmembers were killed, and the airplane was completely destroyed.

• Consolidated-Vultee P4Y-2: Fatigue cracks in the wing structure. On July 18, 2002, the airplane was maneuvering to deliver fire retardant over a forest fire near Estes Park, Colorado, when its left wing separated from the airplane. Both flight crewmembers were killed, and the airplane was destroyed. An examination of other Consolidated-Vultee P4Y-2 airplanes revealed that the area was difficult to inspect because of its location relative to fuselage structure. (NTSB report)

It seems odd that the FAA cited these three crashes as justification for the new rules, but wrote them so that they do not apply to air tankers.

Some of the currently used air tankers that have a maximum takeoff weight of greater than 75,000 pounds include:

• C-130J (turboprop engines)
• P-3C Orion (turboprop)
• 747 (turbofan engines)
• P2V (Cyclone Turbo-compound radial engines)
• DC-10 (turbofan engines)
• BAe 146 (turbofan engines)

The weights of the S2-T and single engine air tankers are well below 75,000 pounds.

Chuck Bushey, who keeps records of wildland fire fatalities, reports that from 1958 through 2009 there were 162 deaths in air tanker crashes, which is an average of 3.11 fatalities each year. Some of these were due to widespread fatigue damage.

Twenty years ago there were 44 large air tankers under federal exclusive use contracts. After the two crashes in 2002 all of the C-130A and P4Y-2 air tankers were grounded and the 33 remaining large air tankers had to undergo an improved inspection program before they returned to active service. Today there are only 18 large air tankers under federal exclusive use contracts.

The U.S. Forest Service estimates that “by 2012 the remaining air tankers will be either too expensive to operate or no longer airworthy”.

We have written before about the state of the air tanker fleet and offered some suggestions for improvement.

Here is a video of the crash of the C-130A near Walker, CA on June 17, 2002:

Bill Moss sent us a photo of the Wildfire Today mug that he won for sending us photos of the test of Tanker 40, the BAe-146 jet-powered airliner that Neptune Aviation is converting into an air tanker. Thanks Bill!

Tanker 40 is currently parked in Neptune’s hangar at Missoula, MT and still has not passed the retardant drop grid tests. HERE is a list of articles we have written that mention Tanker 40. Articles mentioning the BAe-146 air tanker projects are HERE.

Having become interested in the drop patterns of firefighting aircraft, we contacted the United States’ Interagency Air Tanker Board (IATB) that evaluates the performance of air tankers and requested the results of the tests that were conducted for them by the U. S. Forest Service’s San Dimas Technology Development Center. The chart below compares the drop pattern characteristics of seven different air tankers and one drop from a helicopter’s Bambi Bucket. The darkest color represents the heaviest coverage, at 8 gallons per 100 square feet. Lighter colors have less retardant coverage. Click on the image to see a larger version.

I found the differences between the drop patterns of the DC-10, 747, and the MAFFS II to be interesting. The 747 was pretty uniform while the DC-10’s pattern had more variability. The MAFFS II, the latest version of the slip-in system for the military-operated C-130 aircraft, had a much more narrow pattern and more areas of lighter coverage. But the C-130 dropped about 3,000 gallons while the DC-10 and 747 each dropped about 12,000 gallons in the tests.

One of the factors affecting the uniformity of the patterns is the design of the tank system on the aircraft. Both the MAFFS II and the 747 have tanks that are pressurized by compressed air. The pressure forces the retardant out of the tanks through nozzles at a constant flow, while the DC-10 has three tanks attached to the bottom of the aircraft that are modified versions of the tanks produced by Erickson for their Air Crane helicopters. Doors open on the bottom of the DC-10 tanks and gravity pulls the retardant out.

The BAe-146 jet-powered air tanker being developed by Neptune Aviation in Missoula, Tanker 40, appears to have a pressurized constant flow system. Neptune conducted some drop tests of the aircraft in Missoula this summer. Wildfire Today has learned that the aircraft was not able to obtain adequate line lengths for the higher coverage levels. The company has gone back to the drawing board in order to modify the system to increase the flow rates in order to meet the standards.

Minden Air Corp. at Minden, Nevada is also converting a BAe-146 into an air tanker, Tanker 46, but they have not scheduled drop pattern grid testing for the aircraft.

Grid testing involves setting up 800 to 3,000 cups on the ground. After the air tanker or helicopter drops over the cups, the amount of retardant or water in each cup is measured. The cups in the photo below, which were set up for a test, were overrun by cattle. It took several days to straighten the stakes and replace the cup holders.

We were cautioned by the IATB, regarding the tests, that:

• A direct comparison is not always intuitive from these recorded patterns. Close study is required to understand continuity and density for the pattern and determine if the pattern meets the established standards.
• The patterns displayed from the grid testing provide a comparison to the standard set by the Interagency Airtanker Board but do not always translate directly to how the system performs in the field. How the fluid exits the aircraft (under pressure, by gravity, in a block or in a column) can be a significant reason for differences in performance of tanking systems.Terrain, cross wind, gusts, drop height, speed of the aircraft and other conditions may also affect the retardant as it travels to the ground and into the vegetation.

The state of Victoria brought the DC-10 Very Large Air Tanker to Australia during their summer for the 2009-2010 fire season to test the effectiveness of the 12,000-gallon aircraft on down-under bushfires. The ship is operated by 10 Tanker Air Carrier in California and has been previously tested and approved by the Interagency Air Tanker Board for use on fires in the United States.

The Bushfire Cooperative Research Centre tested the DC-10 on one wildfire and five planned missions, identifying serious deficiencies which led to the decision by the Victorian government that:

…the aircraft would be less effective in suppressing Victorian bushfires and would not be suitable for use around the urban interface where the forest meets communities of relatively high populations.

Some of the issues pointed out in the 91-page report that led to that decision included:

Billowing. The drop cloud released by the DC-10 is not uniform. It has thick and thin sections which leave areas on the ground with insufficient coverage.

The tests by the U.S. Forest Service’s San Dimas Technology Development Center led to the same conclusion, as shown in this graphic from their evaluation in 2006. The red areas designate insufficient coverage.

Damage. During one planned test in Victoria the retardant impacted a Eucalyptus forest with such force that it broke off a number of trees with diameters of 4 to 10 inches. While the researchers did not have adequate equipment to accurately determine the drop height, it is thought that the aircraft was at less than the 150-foot height that was requested, which meant that the retardant was still moving forward, rather than straight down, when it impacted the forest. Most air tankers drop at a slower speed than the DC-10’s 150 knots, resulting in less chance for impact damage from the retardant. If the drop had been made at 150 feet, there would have been less damage, but apparently the Aussies do not have confidence that the DC-10 pilots can be depended upon to always drop above the minimum specified height. The government’s concern is:

…the potential to cause serious injury should the load fall on a person. There was also the potential for the aircraft to destroy the property it was attempting to protect.

Some other jet-powered air tankers drop at slower speeds. The BAe 146-200, if it ever appears over a fire, is expected to drop at 115-150 knots. The Russian Be-200 drops at 107 knots while the 747 Super Tanker drops at 140 knots. Multi-engine propeller-driven air tankers typically drop at 100-130 knots, while single engine propeller-driven air tankers drop at 104 knots.

Accuracy. In one planned test, the DC-10 pilots completely missed the fire area. A live fire was set in an area that had been prepared with black line, with burned buffers on the perimeter. Their drop, which was accurately designated by a preceeding lead plane’s smoke, was supposed be across the head of the fire but fell totally outside of the fire area, having no effect. Other drops were more accurate, except for a tendency to sometimes begin or end drops a little too early or too late.

Cost: A report by Deloitte found that the cost of the DC-10 was significantly higher than other aircraft.

Base: There is only one airfield in Victoria where the aircraft could land and take off. Smaller air tankers have multiple options.

NOW WHAT?

From a Victorian government press release :

Two new faster and more flexible large fire bombing planes will be trialled as part of Victoria’s firefighting arsenal which will also be boosted by the use of night vision helicopter goggles and infrared imaging technology.

Environment and Climate Change Minister Gavin Jennings today announced that the Victorian Government would invest $12 million for two new Convair 580 fire bomber planes, a new Erikson Aircrane and four extra fixed-wing aircraft for the upcoming fire season.

The new aircraft will join Erikson Aircranes Elvis and Elsie and bring Victoria’s aerial firefighting arsenal to 48 with a further 170 aircraft on standby if required.

Thanks Chuck