From Cargo Door Failures To One Of The Most Reliable Aircraft – The DC-10
From Exploding Cargo Doors To One Of The Most Reliable Airliners – The DC-10
Throughout history, aviation authorities grounded 8 aircraft. Many of them were true pioneers and brought something new the first time they lifted off the ground.
For example, the Lockheed Constellation was the first pressurized aircraft that saw commercial usage. The de Havilland Comet was the first commercial jet, bringing the world close together with an engine type that initially nobody believed in. But while it proved to everyone that commercial jet travel was the future, it also brought several disasters related to a design issue.
And of course, the one aircraft that changed everything. The jet that shortened the distance between London and New York to 3 hours on a flight – Concorde. While it certainly brought a revolution with it, the type was grounded for a year following a crash in Paris.
Most recently, following two deadly incidents, aviation’s regulators grounded the Boeing 737 MAX in March, sparking the debate whether the type will be canceled. However, with Boeing’s persistence, the aircraft seems to be on track to fly again in 2019.
But the 737 MAX was not the only grounded Boeing aircraft. The Boeing 787 Dreamliner was told to stay put in 2013 after several 787’s operated by ANA and Japan Airlines showcased a design flaw with the battery design. The aircraft has also recently shown up in headlines, showcasing Boeing’s negligence when building the 787.
Nevertheless, there was one more aircraft. Sure, it was not revolutionary like the Concorde or the Comet, but it certainly has brought something to the table and reliably serves airlines to this day, even after 48 years after its first test flight.
It's name? The McDonnell Douglas DC-10 or just DC-10 for short.
The history of the DC-10
The now-defunct and operating under Boeing‘s name manufacturer, McDonnell Douglas had built the DC-10.
At the time, in the late 60‘s-early 70s, Boeing did not compete with Airbus. Airbus had just launched it‘s first commercial jetliner in 1972, but it struggled early on to make sales in the United States.
Boeing competed with Douglas, which was later merged with McDonnell and subsequently was renamed to McDonnell Douglas.
For a short period of time, Lockheed also provided some competition with the L-1011, but the aircraft had its fair share of issues, which prevented it from dominating the United States aviation market.
Anyways, Boeing went head-to-head with Douglas. After the Second World War, aircraft named DC captured a huge portion of the civil aviation market.
However, as soon as the jet age began in commercial aviation, Boeing started out very strong with the Boeing 707 in 1958. Slowly, but surely Boeing started to take over the skies above the US and even around the world.
Initially, Douglas was not fascinated by the Comet or jet-powered aircraft, as they thought it was just a fad that would go away. Plus the groundings certainly did not help, as everybody still believed the Comet’s problems were related to its jet engine.
But, as Douglas realized how far ahead Boeing was, the company started playing catch up. Convincing airlines to order a commercial jetliner was difficult enough, Boeing made the job that much more difficult when they successfully showcased the 707 to airline executives.
However, Douglas had just recently released their DC-7, a piston-powered aircraft, and thus it was difficult to come up with a new jetliner quickly.
Nonetheless, in 1958, Douglas began testing their first jet-liner – the DC-8. Three years prior, Boeing already showcased a flight-capable 707 prototype called the 367-80.
Maneuvering around Boeing
While the article is focused mostly on the Douglas DC-10, you’re probably asking why I am telling you the story of the DC-8 and the Boeing 707.
It’s important to understand the current situation at hand, as Douglas essentially was late to the jet-engine party. They had to make moves around Boeing’s decisions. That’s how the DC-9 started – by undercutting Boeing with the intent to dominate the regional airline market.
But the DC-10 had a different backstory. At first, it started out as a military aircraft for the Air Force. The USAF approached Douglas, Boeing, and Lockheed for an aircraft capable of transporting lots of equipment. Lockheed won the contract.
So, Douglas and Boeing questioned themselves on what to do.
After the very successful debut of the 707 and rising passenger numbers, airlines wished for more. More range, more passenger room and more aircraft generally. Thus, widebodies were born. Boeing was first and announced the Boeing 747, an icon that still flies today. The aircraft could fit from 374 to 490 passengers, depending on the airline configuration.
Airlines were ecstatic, especially the now-bankrupt Pan American. The airline immediately ordered 25 Boeing 747s and heavily influenced how Boeing designed the aircraft.
However, some were cautious. So, McDonnell Douglas had an open market with no competition to work in and a customer – American Airlines (A1G) (AAL) had decided not to take a risk with the 747, as they did not think they would fill the seats on a 747 to justify a purchase of such a jet. While eventually, they did purchase some, they were definitely not as excited as Pan American. Maybe they were right, as American Airlines (A1G) (AAL) is still alive to tell the tale.
DC-10 vs L-1011
Suddenly, there was competition, as Lockheed had begun designing and building their own tri-jet.
Nevertheless, Lockheed had not built a commercial airliner since the Electra, which was last produced in 1961. Even then, the Electra was powered by a turboprop engine. They had a big task on their hands to develop a jet-powered commercial airliner.
On the other hand, Douglas had plenty of experience in building passenger jets. The DC-8 and DC-9 programs had provided them with enough background information to move quickly in the development process.
They did not go overboard, unlike Lockheed. McDonnell Douglas focused on providing a simple, reliable and easy to understand aircraft design based on the previous jets.
While Lockheed‘s design was arguably much more advanced, as the L-1011 had such features as an autoland system, it also required more time and resources. And when competing, sometimes you don‘t have the luxury to tell your customers that you‘ll have to wait or pay more to justify Lockheed‘s massive spending bill when developing the L-1011.
Interested in the story of the Lockheed L-1011? Read our article about it right here!
That‘s where the DC-10 had gained an advantage. Finally, McDonnell Douglas releases a jet before their competitors do. While their prices were identical according to an old Flight International magazine edition from 1972, the DC-10 had just developed quicker.
Thus, American Airlines (A1G) (AAL) in 1968 announced they would order 25 new DC-10‘s. The announcement shocked Lockheed. But in doing so, Douglas had to offer AA a significant discount, which they happily did, as they wanted to make sure their jet is the number one priority for airlines.
In addition, Douglas offered more versions of the DC-10. In total, there were 9 different DC-10 variants.
Douglas offered more flexibility with their airliner fitting a variety of domestic and international markets, while Lockheed could not do so at first.
With American Airlines (A1G) (AAL) and United Airlines securing the future of the DC-10 with their orders, Douglas started the DC-10 production in January of 1970. After adjusting their manufacturing process, the company showcased the first DC-10 to the world in July of the same year. More customers lined up for the newest jet and Douglas now were certain that the aircraft is a success amongst airlines.
The previous year the company also announced the DC-10-30, which became the most popular variant of the tri-jet. Out of the 386 DC-10s that McDonnell Douglas had built, 206 of them were the -30.
But when testing the DC-10 in 1970, engineers have discovered that their cargo door design was faulty. As they pressurized the cabin, the cargo door went flying and the floor, separating the passenger cabin and the cargo hold failed.
But why did the DC-10 cargo doors fail?
In order to save weight, the cargo door locking mechanism was changed from a hydraulic actuator to an electrical one. This was new for Douglas, as they operated a hydraulic actuator on their older DC-8s and DC-9s. As a result, it was less reliable.
However, there were a lot of fundamental design flaws in the DC-10, especially with the cargo doors.
Failure of the aircraft doors
Every single passenger jet is split into two. Passengers are seated on the upper section, while cargo is loaded into the lower part.
But what differs is the position of the wires, cables and hydraulic lines. For example, on the Boeing 747, they are placed above the passenger cabin, in the ceiling. In contrast, the DC-10’s control cables are located under the floor. Which means that any damage to the floor that separates the passenger compartment and the cargo area will hinder the pilot‘s ability to control the aircraft, which can potentially lead to a fatal crash.
Why is this important?
It all comes back to the DC-10’s cargo door. As passenger aircraft fly in really high altitudes to achieve the best efficiency possible, the cabin needs to be pressurized, so that the passengers could breathe. But the cargo area also needs to be pressurized, as the pressurization process adds excess loads to the cabin floor. However, because the cargo bay is also pressurized, the forces are equal, thus the floor doesn’t collapse.
If suddenly a door on either the passenger cabin or the cargo area blows open, the floor will fall apart. While the chance of such a thing happening is very rare, the result of one of the doors saying goodbye to the aircraft can be fatal.
Especially if the aircraft’s main controls are located under the floor, which would collapse in such case.
A cargo door on a passenger is larger than the door opening itself, so it’s impossible to open the door while mid-air, as the pressurization, prevents you from doing so. Even though some have attempted to open the doors while in the air, you’d have to have the force of Hulk to do so.
DC-10 Cargo doors faulty design
But the cargo latches present a different story, as different manufacturers have used different cargo door designs in the past.
Lockheed, the competitor to McDonnell Douglas at that time, designed the door similarly to the passenger one. It was bigger than the opening itself and the door was heavier than on the DC-10.
The DC-10 had used a very similar system to car boot or trunk. When you open your car boot, you can see on the boot that there is a latch. When you close it, the latch attaches to a metal loop in the car frame, thus making it impossible to open while the car is locked or you are driving it.
The DC-10 used a similar system, except of course it had several loops to shut the door securely.
So why did the DC-10 cargo doors would explode?
Firstly, the electric actuator, which controlled a shaft that moved and thus the latches are hooked onto the metal loop and the door would stay closed. As the mechanism reaches the center, the latches stay put because of the forces of pressurization. But if it does not reach the center for some reason automatically, the design of the electrical actuator prevents any manual movement of the shaft to properly lock the door.
Secondly, the lock mechanism was not strong enough. If the mechanism was not properly adjusted, the locking handle, which completely shuts the door, would be able to close. However, the door would not be fully latched, thus at certain altitudes, it would blow out.
And as a result, the cargo area would lose pressure, then the floor would collapse and then the pilots would lose control of the plane, as the aircraft‘s controls are in the floor between the two compartments.
While Douglas did make changes after the 1970 test, where the doors blew out, they were not enough. Simply put, the system was still faulty.
On American Airlines Flight 96, shortly after the American Airlines DC-10 had taken off from Detroit‘s Airport, a cargo door at the back of the aircraft blew open.
Luckily, the aircraft was only partly occupied – only 67 people were on board. So the floor collapsed only partially, thus the pilots had retained some of the control and landed back at Detroit safely.
After the incident, the NTSB told McDonnell Douglas to implement two changes to the DC-10:
First of all, to strengthen the locking mechanism. Secondly, to install a vent at the back of the aircraft.
The NTSB designated the FAA to force Douglas to make these changes. The aircraft manufacturer changed the locking mechanism, but behind closed doors, the two parties agreed that a vent installation would complicate things.
That decision was fatal to 346 people two years later.
In 1974, a Turkish Airlines DC-10 had just landed in Paris after stopping on the journey from Istanbul to London. As personnel on the ground refueled the aircraft, they also loaded and unloaded some cargo.
As the aircraft took off for its second leg of the scheduled service to London, the very same thing happened – the cargo door burst open, the air pressure inside the cabin dropped, the floor collapsed and subsequently, pilots lost the control of the aircraft.
Outcome of the Turkish Airlines Flight 981
McDonnell Douglas eventually lost a lawsuit worth over $18 million to the victims’ families. The aircraft manufacturer tried to direct the blame elsewhere – blaming the FAA for not issuing an airworthiness directive, blaming Turkish Airlines of improperly implementing the locking mechanism modifications and blaming General Dynamics for the poor design of the cargo doors.
Nevertheless, none of this had worked and McDonnell Douglas had to pay the $18 million.
On the technical side of things, a complete redesign of the locking mechanism followed. The FAA finally held its ground, issued an airworthiness directive and ordered a vent to be installed in the cabin floor, in order to prevent the loss of pressure destroying the cabin floor.
After the Turkish Airlines Flight 981 crash and the subsequent changes, the DC-10 never experienced another cargo door blowout.
But its reputation was shaken, as people were nervous when getting on board a DC-10. Nevertheless, the aircraft continued to fly successfully.
Yet that was about to change.
5 years later after the Turkish Airlines flight, an American Airlines DC-10 on Flight 191 crashes just outside Chicago.
DC-10 Engine separation
The crash occurred on the 25th of May, 1979. On June 6th, the FAA grounded the aircraft. The cargo door did not explode this time.
What happened was, that the left side engine separated from the aircraft, punctured critical hydraulic lines and the aircraft subsequently stalled, as it began rolling to the left. The DC-10 slammed to the ground, killing 271 people on board and two people on the ground.
However, the FAA‘s actions were swift and harsh, as no ferry flights would be able to take place during the grounding. In contrast, the Boeing 737 MAX was still able to conduct ferry flights around the United States.
After the NTSB concluded the investigation, the board acquited the DC-10, as the fault lied at the hands of American Airlines (A1G) (AAL) ‘ maintenance procedures. Improper engine maintenance caused structural damage to the pylon, which holds the engine together with the wing.
At this point, the DC-10‘s reputation was shattered. The media had released many pictures of the aircraft flying without an engine and photographs depicting the fireball resulting from the crash.
If people were already double-questioning themselves about getting on a DC-10, after the American Airlines Flight 191, the message was clear – people refused to get onto a DC-10.
Lessons for the future
Looking back at the DC-10 misfortunes and loss of lives, there are a lot of similarities with the current situation of the Boeing 737 MAX.
Corner cutting, the manufacturer‘s and FAA‘s negligence played a big part in the accidents.
Even then, after several deadly accidents, the DC-10 became one of the statistically safest aircraft in the air. Even now, after almost 50 years from the first test flights, you can still see a DC-10 in the sky. But they only fly cargo, as the last passenger flight landed in 2014.
What the story of the DC-10 showcases, that even after initial tribulations and difficulties, an airliner can still serve the passengers safely.
And that‘s what you have to remember when people discuss a crash – that these very freak accidents that happen very rarely. Thousands upon thousands of flights leave daily and the aviation industry is regarded as the safest way to travel from point A to point B.
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