For all of us piston-era airliner fans, I am interested if anyone has information on or thoughts about the three Northwest Airlines DC-7C crashes that happened in a relatively short time frame in the early-1960s. They all happened in circumstances related to icing and the unreliability of the Wright R-3350 engine. They were as follows:

NW001, Okinawa-Manila, July 14, 1960: Airplane was cruising in marginal weather at FL180. After rapid manifold pressure drop on the number 2, crew suspected carburetor icing. It turned out that the supercharger on the number 2 disintegrated while in high-blower, which contaminated the oil, which disabled the propeller governor, which caused a runaway propeller and engine fire. The crew opted to ditch, and 57 out of 58 passengers survived.

NW293, McChord AFB (SEA) – Elmendorf AFB (ANC), October 22, 1962: Crew filed to fly at FL140, which was the preferred altitude as you could operate with the superchargers in low-blower, which improved engine reliability. After encountering icing, the crew requested FL200. Because they had picked up significant airframe ice, and because they were very near MGTOW even without the ice, they had to switch to high blower and climb at METO power. At the top of climb, the supercharger on the number two engine disintegrated, causing oil contamination, the failure of the propeller governor, a runaway propeller, and engine fire. The crew opted to ditch, and everyone on board survived.

NW293, McChord AFB (SEA_ - Elmendorf AFB (ANC), June 3, 1963: Crew filed to fly at FL140, as they were at MGTOW and wanted to operate in low-blower. There was a clear area between layers at 14,000 and 18,000, and they hoped they could operate at 14,000 the whole way. After picking up significant icing, they asked for clearance to FL180 half way through the flight. ATC refused because of conflicting traffic. Not long thereafter, the airplane crashed into the ocean, inverted and intact at a slightly nose down attitude. There was no distress call, and all onboard were killed. The hull sunk to 8,000 feet below sea level, and the crash has never been solved.

All information from the NTSB reports on the 3 accidents.

I have a few questions:

1. Do any posters on this board have memories, information, or ideas about this string of accidents and the repercussions that followed?
2. How did icing impact long haul operations in the piston engine era, when airplanes were significantly speed and altitude limited compared to jet aircraft? In particular, I wonder if the third incident was the result of icing, where the airplane became uncontrollable as a result of airframe icing, causing the crew to lose control before they could declare an emergency.
3. How did crews’ effort to mitigate the reliability problems of the R-3350 engine on DC-7 and Super Constellation aircraft impact the rest of the operations process, especially related to icing? Crews clearly wanted to reduce engine stress by running the engine’s two-speed supercharger in its low gear. But this put airplanes down at low altitudes on long haul flights, giving them greater exposure to weather.

Thanks in advance for ideas!

On NW001, Okinawa to Manila I can provide some additional color from an NWA Pilot Retirees magazine. The flight conducted an emergency decent with a magnesium fire due the runaway prop and super charger issues, The fire extinguishers worked originally but the fire started again leaving the crew little options but to ditch the aircraft at night in a rainstorm. The Captain was David Rall. This was, at the time, widely proclaimed as one incredible feat of airmanship. And it was. The co-pilot called out when he saw the water from his open cockpit window. There was no time but to flare the plane for the ditching. All survived. One person later died before rescue. The USAF used Albatross seaplanes to rescue the passengers and crew. They had trouble with fouled spark plugs due to the water and had to water taxi considerable distance due to the engines not developing full takeoff power.

What type of ice protection was available on the DC-7?

CATIIIevery5yrs wrote:

What type of ice protection was available on the DC-7?

Carb heat and carb alcohol in the engines. I don't know about for the airframe. My guess is electrical heating on the leading edges?

JTPaint2 wrote:

On NW001, Okinawa to Manila I can provide some additional color from an NWA Pilot Retirees magazine. The flight conducted an emergency decent with a magnesium fire due the runaway prop and super charger issues, The fire extinguishers worked originally but the fire started again leaving the crew little options but to ditch the aircraft at night in a rainstorm. The Captain was David Rall. This was, at the time, widely proclaimed as one incredible feat of airmanship. And it was. The co-pilot called out when he saw the water from his open cockpit window. There was no time but to flare the plane for the ditching. All survived. One person later died before rescue. The USAF used Albatross seaplanes to rescue the passengers and crew. They had trouble with fouled spark plugs due to the water and had to water taxi considerable distance due to the engines not developing full takeoff power.

Wow that is amazing about the Albatross. How far did they have to water taxi? To ships nearby so they could do spark plug changes when conditions improved?

Yep the NW crew was just fantastic - the pilots and the flight attendants. The pilots decided to close the firewall valves to cut off oil to the engine to force it to cease in order to stop the windmilling propeller. That was probably a good idea in a bad situation, but it ended up causing the prop to shear off and penetrate the cabin. But the flight attendants had already gotten everyone out of the DC-7C's forward cabin. Can you imagine for passengers who originated in New York and who flew half way around the world through Seattle, Alaska, Japan, and Okinawa, and ended up treading water in the Pacific?

I always wondered why the airlines got rid of their DC-7's so quickly - thanks for the interesting stories

CATIIIevery5yrs wrote:

What type of ice protection was available on the DC-7?

The DC-7 used thermal airframe icing protection from the engines, props were electrically protected, R-3350 TC engines used a unique induction system to control carburetor icing and heat. Well protected airframe and engines.

This accident is weird. Maybe pitot tube ice or unreliable airspeed caused disorientation of the pilots.

The turbo compound engines were a mess and very temperamental. Transoceanic diversions were always happening due to engine failures. The high costs lead to early retirement of the 7s and Connies.

The 7C was a magnificent long range airplane in it's day and fast too!

JTPaint2 wrote:

CATIIIevery5yrs wrote:

What type of ice protection was available on the DC-7?

The DC-7 used thermal airframe icing protection from the engines, props were electrically protected, R-3350 TC engines used a unique induction system to control carburetor icing and heat. Well protected airframe and engines.

This accident is weird. Maybe pitot tube ice or unreliable airspeed caused disorientation of the pilots.

The turbo compound engines were a mess and very temperamental. Transoceanic diversions were always happening due to engine failures. The high costs lead to early retirement of the 7s and Connies.

The 7C was a magnificent long range airplane in it's day and fast too!

Thanks for the info! I really enjoy learning more about the last generation prop liners.

MohawkWeekend wrote:

I always wondered why the airlines got rid of their DC-7's so quickly - thanks for the interesting stories

As others have said, part of the reason the airlines got rid of their DC-7s so quickly was because its engines were unreliable. AA did not serve DEN pre-deregulation, but their DC-7s diverted to DEN so many times due to engine failures that they kept spare engines there.

The DC-6 was more reliable, and required less maintenance, so airlines chose to keep their DC-6s and phase out their DC-7s. Although the DC-6 was slower than the DC-7, the speed difference between a DC-6 and a DC-7 was very small when compared to the speed difference between DC-6s / DC-7s and pure jets, especially on shorter routes like LAX-PHX and DEN-OMA.

WA707atMSP wrote:

The DC-6 was more reliable, and required less maintenance, so airlines chose to keep their DC-6s and phase out their DC-7s.

Fifty years ago there was a joke telling:

DC-6 - a four engined plane with three blades propellers
DC-7 - a three engined plane with four blades propellers

I just sat in a DC-7B cockpit with my father for an hour as he went over all the systems. The 7 and 7B used janitors heaters for the airframe. It had quite a few on board. The panel for them was above the carts head. As for the 7C, I would think they were similar to the 7/7B but do not know for sure. It was a different beast.

Cheers.

prebennorholm wrote:

WA707atMSP wrote:

The DC-6 was more reliable, and required less maintenance, so airlines chose to keep their DC-6s and phase out their DC-7s.

Fifty years ago there was a joke telling:

DC-6 - a four engined plane with three blades propellers
DC-7 - a three engined plane with four blades propellers

I believe the Lockheed Super Constellation was known as Lockheed’s best 3-engine airliner. Maybe the Super Constellation was mis-named. It should have been the Lockheed Tri-Star!

TW870 wrote:

CATIIIevery5yrs wrote:

What type of ice protection was available on the DC-7?

Carb heat and carb alcohol in the engines. I don't know about for the airframe. My guess is electrical heating on the leading edges?

One thing I find odd: one would think that an engine in this performance and power class would have been fuel injected. Was the technology not yet ready? I know the Wright engines were finicky and were skirting the edge of what could be done with piston engines, but in my layman’s view, FI would have been a better option.

JTPaint2 wrote:

This accident is weird. Maybe pitot tube ice or unreliable airspeed caused disorientation of the pilots.

Excellent hypothesis. The fact that the airplane was inverted and intact on impact indicates some kind of spatial issues, and not just a mechanical problem such as the engine failures and runaway props that caused the other two accidents.

It also seems that the desire to run the R-3350 in low blower - which required lower altitudes - put crews in difficult situations with icing. In both Flight 293 accidents, the crews knew there were higher altitudes available that seemed to be clear of icing, but wanted to start out down low just so they wouldn't have to run the engines at higher power settings. The decision to start off at FL140 touched off the accident sequence in both cases - even though it was standard procedure and I would have made that decision as well.

The other thing it seems like they needed to train pilots more clearly on how to respond to power drops while in cruise. On both of the ditchings, the crew mistook a manifold pressure drop for carb ice. But in the intervening time interval when they were adding carb heat and alcohol, the superchargers were coming apart, which contaminated all the oil with parts, which in turn disabled the propeller controls. Neither accident would have happened if they had feathered the prop right away when they saw the manifold pressure drop. I understand, though, that with engines this unreliable, if you feathered at the first sign of trouble, you would divert on basically every flight.

Bottom line is that this is why the -7s and the Super Connies had to go - as cool as they were!

The Boeing Stratocruiser was also labeled a "3 engined airliner" due to inflight shutdowns on those huge engines and associated propeller issues.
I lived on Guam for 8 years while my father was stationed there, and I remember Pan Am stored Strat engines in a US Navy hangar next to my father's detachment unit. Flights arrived at USN Air Station Agana and Pan Am had a small quonset hut terminal building, but no hangar. All maintenance was conducted in the open unless the plane could be towed to a vacant hangar. My Dad said many times people never thought anything bad about Pan Am and its aircraft issues, but the first hiccup with a Transocean DC-4 would send people howling for that "fly by night outfit" to be shut down.
He flew DC-4's (R5D's) in the military and always said they'd get you home in one piece, but didn't want to fly on a Strat.

TW870 wrote:

/[quote="JTPaint2

Bottom line is that this is why the -7s and the Super Connies had to go - as cool as they were!

I was a young lad but, by the early 60s we were ensconced in the jet age. If it had propellers it wasn't cool for the travelling public of course excluding us. As a matter of fact National "Airline of The Stars" Pre Sun King declared itself an all jet fleet. Of course they had a bird with propellers the Prop Jet Electra so, DC7,DC6 Connies etc were old news and filtering down to the used airliner second and third tier airline and cargo companies. As mentioned, there were teething problems with the new pure jets that in turn caused their share of loss of like accidents.