POSSIBLE CAUSES OF THE
BAKERS CREEK CRASH
From various sources I have been able to formulate what I believe happened that fateful day. Some of what follows is factual; some is speculation. I’ll try to differentiate between the two.
It was very foggy at the Mackay airport that morning. Take-off time had to be extended. Finally, at about 6:00 A.M. the B-17C took off toward the southwest. Approximately two minutes later, the aircraft crashed south and a little west of the airport.
Two Australians with whom I corresponded claimed they saw abnormally bright and long exhaust flames coming from an engine soon after the aircraft became airborne. Both also reported hearing loud popping sounds that one described as backfiring. The latter, a then-19-year-old farm girl living directly west of the airport, was rounding up milk cows, a daily chore she had been doing for an undetermined period of time. She had become accustomed to the sights and sounds of aircraft taking off and knew what to expect. On that particular morning she realized something unusual other than the exhaust flame and popping sounds: the B-17C was flying level and not in the nose-high attitude it normally assumed following lift-off.
A third Australian sent a map of the Mackay area on which he indicated the normal flight path of the aircraft departing for northern destinations. After becoming airborne the aircraft would bank (turn) right and head north. On 14 June the B-17C did not bank right. It first made a 90 degree left bank and flew approximately south before making another 90 degree left bank. It reportedly leveled out before settling among some trees and bursting into flames.
Another Australian made a sketch of the crash scene as he remembered it. He was a 14-year-old teenager in 1943 living with his parents near the crash site. He, along with his father and uncle, was among the first to reach the crash scene. His sketch, drawn about 50 years later, was judged to be remarkably accurate by others who had also seen the crash scene.
The sketch shows, and is annotated to explain, that the aircraft contacted the trees in a wings-level attitude, mowing down the vegetation in a progressively lower pattern as it settled to earth in a gliding fashion. The right wing struck a large tree limb or trunk and was torn off. The fuel load of several hundred gallons, carried in the wings, was set afire. The tail section and rear fuselage broke away, but the main part of the airplane was either consumed by the fire or became a mass of jumbled wreckage. Two passengers, believed seated in the section that broke away, were alive when the first rescuers arrived. An ambulance arrived and both men were rushed to the Mackay hospital, but one died en route. Miraculously, the only survivor was not seriously injured. He suffered some minor cuts and abrasions and a few burns but was able to return to duty in a relatively brief time. Many years later it was determined two ribs had been broken.
The foregone narrative is believed to be a factual account of what transpired that Monday morning, 14 June 1943.
What caused the airplane to crash? That question has “bugged” me more than anything I’ve ever tried to answer. Nothing has occupied my thoughts as intently and deeply – or as often. When one devotes incalculable time concentrating on a subject, as I have done, certain conclusions are formed. It is my belief that the primary cause of the crash was a substantial loss of power in at least one engine. A contributing factor may have been an over-loaded aircraft, or at least too much weight aft of the center of gravity.
What qualifies me to arrive at such conclusions? Most of my 26 years military service was spent directly or indirectly in the aircraft maintenance field. About half those years was in flying organizations; the other half in the technical instruction area. In the latter case I was almost invariably in a supervisory or technical writer position and was thus required to do much research to assure that the information presented to students was accurate. When the Air Force in 1954 established various career fields to cover the multitude of jobs required to function as a military branch, I was given a choice of aircraft maintenance technician, aircraft electrical technician or reciprocating engine technician. I chose the latter because it was the most challenging. Experience had shown that the majority of aircraft problems consisted of engine malfunctions.
Not only my “bread and butter” job involved the piston-driven engine. In 1949 I began doing automotive maintenance in my spare time. Within a year or two my interest turned almost exclusively to engine tune-ups. That facet of automotive work required much study into the finer points of engine operation to enable me to diagnose problems. As a result of what I learned, my knowledge and understanding of aircraft engines were greatly improved in the same way that what I had learned about aircraft engines enhanced my comprehension of automotive engines. One complemented the other because both operated on the exact same principles.
Before getting into specifics on the B-17C crash, some understanding of propellers is essential. Although not aerodynamically accurate, suffice it to say the propeller (prop) pulls the aircraft forward. The B-17 utilized variable pitch, constant speed, hydromatic props. That means the angle of the blades could change to maintain the rotational speed (revolutions per minute, or RPM) selected by the pilot. To change to a higher angle (pitch), engine oil under pressure was directed by the prop governor, which incorporated a small gear type pump to further increase the oil pressur, into the prop dome. Inside the dome was an intricately designed mechanism that employed the principle of hydraulics to force the blades to a higher pitch and, thus, take a bigger bite of air. To change the blade angle to a lower pitch, the governor directed oil trapped in the dome to return to the input side of the governor. Centripetal force, the force that tends to impel parts of a rotating thing to move toward the center of rotation, caused the blades to move to a lower angle.
Changing the prop pitch is similar to shifting gears in an automobile transmission. For take-off, the pilot placed the prop control in low pitch, or maximum RPM, position. This compares to the low, or first gear, position of an automotive standard transmission. The aircraft throttle control was pushed full forward to enable the engine to develop maximum power. The prop governor on the B-17 limited the engine speed to about 2700 RPM by causing the prop blades to move to a higher pitch and, thereby, impose a load upon the engine. The engine was thus prevented from exceeding a preset limit. The limiting effect of the governor was reached before the throttle was fully open. The more the throttle was opened, the greater was the blade pitch increase, and the bigger was the bite of air taken by the blades. To prevent the prop blades turning at too high a speed and thus becoming inefficient, the propeller shaft was geared to turn at a lower RPM than that of the engine crankshaft.
After the aircraft became airborne and had attained a safe flying speed, the pilot reduced engine power by retarding the throttle control to a predetermined manifold pressure. He next repositioned the prop control to obtain a lower RPM to lessen the stress upon the engine. The pilot’s action is equivalent to the automobile driver letting up on the gas pedal and shifting the transmission into second gear. Upon reaching the altitude at which he planned to cruise, the pilot again reduced power by retarding the throttle control and then “shifting into high gear” by repositioning the prop control to obtain a still lower engine RPM. In flight the engine speed was actually controlled by the propeller which was controlled by the prop governor.
The foregone technical explanations should help in understanding why I believe engine failure was the primary cause of the crash. There are a variety of ways an engine can fail; some due to mechanical faults, some as a result of operational procedures. Each would require as much, if not more, explanation than that offered to explain the propeller’s operation.
It is an established fact the airplane did not continue to climb after becoming airborne. Gaining altitude as rapidly as possible – especially during foggy conditions – is a cardinal rule of flying. Another vital rule is to not climb at an angle that would cause the plane’s airspeed to decrease to a dangerous point. If the airspeed is insufficient to sustain flight, the aircraft will stall and gravity will prevail. So what does the pilot do if airspeed approaches the stalling speed? He lowers the aircraft’s nose to gain airspeed and, if possible, advances the throttle to increase engine power.
The B-17C that morning was too low to allow a significant increase in airspeed by lowering the nose. The throttles were already full forward, so that option was not available. It is apparent the pilot did the only thing he could do; he tried to maintain flying speed and attempted to return to the airport to make an emergency landing. Why was he unsuccessful in that attempt?
Mentioned earlier was the abnormal exhaust flame and unusual sounds reported by two eyewitnesses. What they saw and heard clearly indicates an engine malfunction, possibly an internal failure. The popping sound one described as backfiring was most likely afterfiring, the explosion of the fuel-air charge in the exhaust manifold. Afterfiring occurs when the fuel-air charge is not ignited in the cylinder and is discharged into the exhaust manifold where the combustible mixture is ignited by the hot exhaust gases from the other cylinders. Backfiring is the combustion of the fuel-air mixture in the intake manifold (induction system) located between the cylinders and the carburetor. Backfiring produces a muffled sound whereas afterfiring is a loud, sharp sound similar to a rifle shot.
One of the most destructive conditions that can happen to an aircraft engine is detonation of the fuel-air charge. Detonation occurs when the fuel-air charge within the cylinder combustion chamber begins to burn following normal spark plug ignition but then explodes, or detonates. All the remaining heat energy of the charge is released in one spot. If detonation continues for only a few seconds, the localized concentration of heat is sufficient to burn a hole in the aluminum piston head. Such damage invariably results in a partial loss of power. If the condition that led to detonation extends to other cylinders, those cylinders would suffer the same fate. If that happens, the power output of the engine would be drastically reduced – if not eliminated.
One of the basic causes of detonation is excessive manifold pressure, the pressure of the fuel-air mixture in the intake manifold. Simply put, the higher the manifold pressure the greater will be the quantity of fuel and air molecules and, thus, the greater will be the heat produced in the combustion chamber with a resultant greater pressure to force the piston downward on its power stroke. Manifold pressure could be boosted by utilizing a turbosupercharger, essentially an air pump driven by engine exhaust gases. The speed of the supercharger impeller determined how much the incoming air was compressed before it passed through the carburetor en route to the cylinders. The impeller’s speed was determined by the amount of exhaust gases diverted to turn the turbine wheel that turned the impeller. A flat, circular valve, called a waste gate, located inside the exhaust manifold within a few inches of the outlet end, controlled the amount of exhaust gases diverted to the turbine wheel. The position of the waste gate was controlled by the pilot through a regulator utilizing engine oil pressure. Each engine was equipped with a separate turbosupercharger and control system designed to improve the engine’s ability to operate in the thinner air at altitude. The turbosupercharger could be used during take-off to increase manifold pressure and thereby increase engine power. There were known cases of superchargers over-speeding with resultant excessive manifold pressure and detonation. It would be only speculation to say that happened on the B-17C, but the possibility exists.
A drop of engine power would cause a drop of engine speed. The prop governor would instantly detect the loss of RPM, oil in the prop dome would bleed out, and centripetal force would move the prop blades to a lower angle to maintain the RPM selected by the cockpit prop control. The lower blade angle would produce less forward thrust because the blades would be taking a thinner bite of air. This sequence of events would occur with each decrease of crankshaft RPM due to a loss of power. A continual loss of power would cause the prop blades to eventually move against the low pitch stops with a resultant minimum of forward thrust. It is possible for the engine power to become so low that the forward motion of the aircraft would cause the propeller to “windmill.” A windmilling prop actually drives the engine crankshaft as well as impose considerable resistance, or drag, on the aircraft’s forward movement. A loss of airspeed results. To reduce the drag of a windmilling prop, the prop is feathered to stop its rotation. Feathering is accomplished by directing engine oil under pressure into the prop dome to move the blades into a streamlined position so that the flat sides of the blades are parallel to the direction of flight. There is no indication a prop on the B-17C was feathered.
One of the eyewitnesses with whom I corresponded wrote about an odd sound she described as being like an automobile stuck in a bog (mud) and the engine racing at full throttle. That sound is indicative of an aircraft propeller in full low pitch and the engine over-speeding. If internal failure of an engine caused a drastic drop or complete loss of oil pressure, the prop governor would have been unable to increase blade angle to impose a load upon the engine to slow it down. It appears that what the lady heard was a runaway prop being driven by an over-speeding engine, a condition that impedes an aircraft’s forward motion.
Mentioned earlier as a possible contributing factor was an over-loaded aircraft or perhaps excessive weight aft of the center of gravity (CG). The CG is the spot about which an aircraft would balance if suspended. Balance of the aircraft is one of the many factors essential to the safe and efficient operation of the aircraft. The total weight of the aircraft must be distributed so that the CG falls within specified limits. When an aircraft is not balanced correctly, several unsafe conditions are produced, such as: increased take-off distance, increased stalling speeds and decreased rate of climb.
The CG of World War II bombers was located in the bomb bay section. It has to be assumed that the CG of the B-17C (40-2072) was maintained as designed by the manufacturer following removal of numerous combat items (guns, oxygen equipment, armor plate, etc.) when it was converted to a troop carrier. The fact the aircraft operated for over a year in its altered configuration is strong evidence the CG was within allowable limits.
But how was the weight of the 35 passengers and their luggage distributed? The survivor told me it appeared each man was loaded down with “goodie” items unobtainable in New Guinea. Passengers boarded the aircraft through a door located near the trailing edge of the right wing. Did each man hold on to his bag of goodies, or was he instructed to store it in the aft section of the fuselage before moving forward? The bomb bay doors had been permanently secured in the closed position, and that section – where the CG was located – was always fully loaded with passengers. A few, probably not more than four, were crowded into the nose section. The remaining passengers, unquestionably a considerable number, were located aft of the bomb bay.
In 1992 when I first became acquainted with Foye Roberts, the only survivor, he explained briefly how he was seated on the floor, facing forward with his close friend seated forward of him. His description reminded me of people seated tightly together as if riding a toboggan. They had no restraining straps or seat belts. I quickly sensed that it was extremely painful for Foye to recall that horrific event, so I never again asked him for information.
The force that enables an aircraft to rise off the ground and remain in the air is called lift. The cross-sectional shape of the wing, the area of the wing, and the speed of the wing through the air all combine to produce lift. The engine provides the power to turn the propeller that provides the forward thrust that pulls the aircraft through the air. The faster the wing moves through the air, the greater will be the lift.
The lift of a wing is perpendicular to the top surface of that wing. When an aircraft is banked (turned), some lift is lost. The greater the angle of bank ( the sharper the turn ) the greater the loss of lift. The loss of lift causes the nose of the aircraft to drop. To prevent a loss of altitude while banking, the pilot raises the nose of the aircraft.
The B-17C pilot was faced with some extremely critical problems and had to make a rapid decision. He obviously knew the aircraft could not remain airborne much longer. The fog prevented his selecting a safe area straight ahead in which a crash landing could be made. He wisely chose to return to the airport surely knowing the aircraft would lose altitude during the two necessary turns. I suspect he elected to lose some altitude rather than risk stalling the aircraft. In addition to the loss of altitude during the two turns, it is very likely the airspeed was steadily declining due to drag caused by the suspected runaway propeller.
Why have I gone to considerable length to explain some aeronautical principles and engine malfunctions? It is an attempt to show how I’ve relied on my background to analyze the facts, as well as the claims, to arrive at a plausible conclusion. It would be an injustice to the flight crew for me to simply “join the crowd” and assign the cause as pilot error. There are too many reasons for me not to conclude that a power loss was the
primary cause of the crash. Following are some facts and a few suppositions that led to my conclusion.
1. First and foremost was the claim by two eyewitnesses that abnormal engine
. exhaust flame and loud engine sounds were seen and/or heard.
2. The sound described by one that indicated a runaway prop and an over-speeding
engine.
3. An inability to gain altitude soon after take-off as evidenced by the level flight . of the aircraft.
4 The pilot making a left turn rather than a right turn toward the original destination.
5 The pilot making a second left turn in what was obviously an effort to reach the . airport for an emergency landing.
6. The aircraft’s landing lights being switched on after becoming airborne. The lights are used to enable the pilot to visually orient the plane’s position relative to the ground and are normally used only while landing.
7. A very strong indication the landing gear were down. That clearly indicates
the pilot planned to land. It is impossible to ascertain if the gear were retracted
following lift-off – standard procedure, especially with a heavy load – and then lowered in anticipation of landing, or if the gear were never retracted. The right main gear was found quite some distance from the bulk of wreckage. The main gear in the retracted position were almost completely encased within the inboard engine nacelles. It would have been virtually impossible for them to be dislodged when retracted.
Some who were familiar with the B-17C’s maintenance history alluded that two engines had recently been replaced and the other two had fairly low flying hours. Such comments obviously are intended to excuse the engines of any complicity in the crash. Anyone who thinks that way is simply not familiar with the intricate internal mechanisms of the aircraft radial engine and its potential for failure if everything does not work in perfect harmony. A new or rebuilt engine – especially the latter – does not guarantee flawless operation, nor does one that has performed satisfactorily for a lengthy time assure continued faultless performance. A personal experience justifies that statement.
In 1948 I was a passenger on a B-29 that was to fly from California to Okinawa. The first leg of the flight was to Hawaii, a flight of about 11 hours. The second leg was a 17-hour flight to Guam. On those two flights the four engines performed flawlessly. The final leg was to be to Okinawa. My seating position was beside the flight engineer, and I closely observed the engine instruments as he meticulously made the various pre-takeoff checks. As before, the engines met all requirements. The pilot moved the plane into position for take-off, advanced the throttle levers full forward and the aircraft began its run down the runway. Within a few seconds the pilot retarded all throttle levers and applied brakes to stop the aircraft. The number three engine was emitting a heavy volume of bluish-white smoke, a sure sign of oil burning which indicated internal failure.
Subsequent inspection of the turbosuperchargers (each B-29 engine utilized two of those units) revealed each had sustained damage to the turbine wheel. Such damage unmistakenly indicated that at least two cylinders had disgorged metallic debris. Half of the 18 cylinders were connected to an exhaust manifold that discharged exhaust gases through one supercharger while the other nine cylinders were connected to a manifold that led to the other supercharger.
We replaced the engine and both superchargers after which the crew chief ran the engine to assure it and the two superchargers functioned properly. A short time later the flight crew took to the air to slow time (break in) the newly installed engine. The aircraft soon landed with number three engine propeller feathered. The flight engineer told us that seven minutes into the flight the engine failed. I don’t recall the cause of the failure. Usually such failures were due to loss of oil pressure with consequent bearing failure. The newly installed engine had to be replaced.
There is no reason to believe faulty maintenance contributed to the crash of the B-17C. I am confident the maintenance crew was well qualified and extremely competent. There was absolutely nothing the mechanics could have done to foresee and thereby prevent the tragedy. The sad fact was the radial air-cooled engine was more susceptible to internal failure than was the V-type or inline liquid-cooled engine due to the more complicated mechanisms required in the radials.
It is impossible to ascertain the exact cause of the crash. Efforts to obtain an aircraft accident investigation report were in vain. It is very unlikely an in-depth investigation was conducted. Even more doubtful is the likelihood that engine tear-down investigations were performed. A thorough, meticulous inspection of components following complete engine disassembly would either have absolved the engines of failure or would have pinpointed the cause if an engine had failed.
Aircraft crashes during WW II were often viewed as part of the cost of “doing business.” Many crashes were either not investigated or were given a cursory “once over lightly” to comply with regulations. The Mackay crash warranted an investigation since so many men perished. It would be very interesting to learn the qualifications of those appointed to conduct the probe. Were they experienced investigators or randomly picked men who were readily available? My guess is they were the latter and probably pilots. If so, then it is very unlikely their knowledge of aircraft extended past the ability to fly one. Pilot training did not include a deep understanding of the internal combustion engine; only how to start and control their operation. Thoroughly competent aircraft accident investigators were extremely scarce.
Those most familiar with the crash seemed prone to blame the pilot. Surely, if those men had been more objective and analyzed the facts, they would have praised the pilot’s efforts to save his precious cargo. Many, many pilots received medals for doing much, much less. I could locate no official records to substantiate my claim that engine failure was the primary cause of the crash. Nor is there any unquestionable proof that the pilot acted irresponsibly; only speculation and accusation that he did.
It is highly doubtful the precise cause of the tragic incident will ever be known. I have offered my long-pondered opinion for your information and evaluation.
Teddy W. Hanks, CMSgt., USAF (Retired)
19 October 2000