National Transportation Safety Board documents, released on Wednesday, reveal a great deal about weight and balance calculations on the de Havilland DHC-3 Otter that crashed in Soldotna last July. The pilot, Walter "Willie" Rediske and all 9 passengers -- two families from South Carolina -- were killed in the crash.
The aircraft was being flown as an on-demand charter for air taxi operator Rediske Air, and was bound for Bear Mountain Lodge, approximately 90 miles southwest of Soldotna. Rediske was also the company owner and director of operations.
Based on a recent insurance application, Rediske had 7,765 total flight hours with 105 hours in the DHC-3. The same form from the previous year indicated a total time in the DHC-3 of 155 hours; it isn't clear why this discrepancy existed.
The DHC-3 was the only turbine aircraft in the Rediske Air fleet, as well as the only taildragger. It is unknown if the pilot had any other taildragger time beyond that in the Turbine Otter.
According to the load manifest out of Soldotna, the passenger weights were totaled at 1,350 pounds, along with 80 pounds of luggage. Bear Mountain Lodge, who chartered the aircraft, also dropped off a load of groceries and other supplies at the Rediske Air office in Nikiski, where the flight originated. The lodge operator estimated the cargo's weight at 300 pounds and he and Rediske loaded the aircraft. The 300-pound figure was recorded on the manifest as the total weight.
NTSB documents reveal that none of the Bear Mountain freight was weighed in Nikiski prior to loading and departure for Soldotna nor was anything weighed there, when the passengers were picked up. This was in clear violation of the company's Operations Specifications, which require Rediske Air "...use only actual weights when determining the aircraft weight and balance."
In more general terms, under part 135.399 of the Federal Aviation Regulations, the company could not operate the aircraft without complying with "the takeoff weight limitations in the Approved Flight Manual or equivalent." In order to accomplish this, accurate weight and balance would have to be calculated at time of loading.
Based on painstaking and long established methods of post-crash analysis of the wreckage, as well as a receipt for a portion of the lodge purchases, investigators established a conservative estimated weight likely closest to the actual weight of the combined cargo onboard of 718 pounds of freight for the lodge and 187 pounds of baggage for the passengers. Despite repeated requests from the NTSB, the lodge did not provide receipts for some items, including a quantity of meat, which were found in the wreckage, so a more accurate weight of the freight could not be determined.
The NTSB calculated six different weight and balance scenarios in its investigation, utilizing a variety of factors to accommodate changes in passenger and cargo weights and placements of baggage. Based on the scenario the report says "more closely approximates the actual weight and balance of the airplane during the accident flight," investigators concluded the aircraft was slightly over the certificated maximum gross weight of 8,000 pounds and -- significantly -- 5.58 inches aft of the center-of-gravity limit. Based on photographic evidence, all of the cargo was in the rear, along with a large portion of the baggage. The two heaviest passengers, estimated at 181 and 218 pounds, were also seated in the rearmost two seats.
This scenario also addressed questions concerning the fuel onboard. The aircraft was equipped to carry 251 gallons in three tanks. A witness observed the pilot topping off the front tank and beginning to fuel the second tank; the witness then departed and it was unknown if that tank was filled or what fuel at all was added to the rear tank. The NTSB thus included only the aircraft flight manual's minimum requirement of 20 gallons of fuel in the rear tank which is certified to carry up to 87 gallons. If the pilot filled that tank, the center of gravity would have been even further aft than the NTSB determined.
Loading an aircraft this far aft, which creates a tail-heavy configuration, makes an aerodynamic stall much more likely. Stalls at low altitude, such as one that might occur during takeoff, are almost never possible to recover from.
As an air taxi operating under Part 135 of the FARs, Rediske Air was assigned a principal operations inspector by the FAA. In an interview with the NTSB the inspector noted that that Rediske "wasn't on his radar" and deemed a "good operator." The inspector visited the company only twice a year; he was also principal operations inspector for 37 other Part 135 operators. When asked why the Turbine Otter was not listed in the Operations Specifications weight and balance program with the company's other five aircraft, as required, the inspector said it was an oversight. The NTSB noted in its report that after the accident, the FAA attempted to insert a revised section of the loading schedule list "that included the accident airplane with a retroactive date."
Alaska aviation is full of stories of overloaded and improperly loaded aircraft dating back to the early days of territorial flying. This passage from "The Flying North," originally published in 1945, is a perfect example of such extremes:
"If the ship'll take her," the pilots say, "we'll fly her." Bunks and poling boats have often been wedged into small single-engine craft. A dredge shaft was once hauled in a Bellanca; the pilot had to take out the front window to fit it in. A small gas tractor was carried in a Stinson. The pilot removed the doors of the plane and flew with the track frame sticking out two feet on either side. "The tail shook a little," he admits. This was no the worst. "If she's too big to get in," they say, "we'll tie her on outside." Pilot Jack Peck once lashed a big cookstove onto the fuselage of his Ryan B-1. A Michigan sled weighing 260 pounds was hauled by Oscar Winchell underneath his Stinson.
These are the stories that gave birth to a legend and then created the ever-popular Bush Pilot Myth. However, they are just stories from pilots long dead who passed tales along in the most casual of settings while creating heroic images of themselves for posterity. Here are some more recent truths concerning faulty weight and balance:
• In August of last year a pilot was killed and his passenger seriously injured when their Super Cub crashed on takeoff from Tatina Airport about 51 miles southeast of Nikolai. The NTSB determined that the aircraft was an estimated 642 pounds over gross weight and the CG was 5.07 inches aft. Further, a set of caribou antlers was attached externally to the left wing strut and a rifle was loaded on the right wing.
• In 2010, a Cessna 206 crashed soon after takeoff from Merrill Field Airport in Anchorage, resulting in the death of one passenger and serious injury to the pilot and three others. The NTSB conservatively estimated the weight of the passengers, cargo and fuel at 658.2 pounds over gross weight. The CG was estimated to range between 3.95 and 8.82 inches aft of the rear-most allowable limit. The pilot told the NTSB he estimated the weight of his cargo and did not actually weigh anything.
• In 1997, a Hageland Aviation Cessna Caravan crashed soon after takeoff from Barrow, resulting in the deaths of the pilot and all seven passengers. In that case the pilot was faulted for his disregard of lateral fuel loading limits. The NTSB noted he had instructed a company lineman to fuel the left wing tank only, resulting in a fuel imbalance between 450 and 991 pounds. The published lateral fuel limit for the aircraft, according to the Pilot's Operating Handbook, is 200 pounds.
• In 1994, a Piper PA-32 operated by Peninsula Airways crashed soon after takeoff from Portage Creek, resulting in the deaths of three passengers and serious injuries to the pilot and one other occupant. The NTSB determined the aircraft was either 411 or 279 pounds overweight -- the discrepancy stemmed from confusion over the actual amount of fuel onboard. In either case, the CG was 3.8 or 3.93 inches aft of the maximum allowable limit. "I have never seen a plane packed so tightly with people and gear -- I remember commenting just before they closed the door they looked packed like cord wood," a witness told investigators in that crash.
There are many aspects of Alaska's environment that are blamed for the state's high aircraft accident rate and often used as excuses for pilot error. The weather and lack of adequate weather reporting, the unpredictable conditions of bush runways, confusing radio frequencies and more. But weight and balance is only and always the flight crew's responsibility. Even if the aircraft is loaded by others, the pilot must supervise and accept that load. As flight students learn early on, there is no assigning of blame when it comes to weight and balance; these are calculations and decisions that belong solely to those in the cockpit.
Although the NTSB's probable cause report on Soldotna will not be issued for at least another three months, the overwhelming focus in the investigative documents on the aircraft's weight and loading is indicative of the agency's interest in it as a significant factor in the crash. In Tatitna, Portage Creek, Merrill Field and Barrow, inadequate weight and balance calculations and improper loading were determined to be the primary causes for each accident, thus creating situations where actions on the ground led to tragedies in the air. There was nothing those pilots could do once they took off; the aircraft stalls and subsequent crashes were unavoidable once the choices were made to load their planes the way they did. It remains to be seen if the Rediske Air crash will be another tragic example of such poor but avoidable preflight planning.
According to the NTSB the final probable cause report on the Rediske Air accident will be released in the next 3 to 4 months.
Contact Colleen Mondor at colleen@alaskadispatch.com.