The McDonnell Douglas DC-9-80/MD-80 series of narrowbody jetliners was the second-to-last DC-9 major version produced (from 1979 through 1999), the second-largest, the most-produced (just under half of all DC-9s ever produced were of one of the five DC-9-80 minor versions), and the last to be powered by the Pratt & Whitney JT8D low-bypass turbofan.

By 1985, however, the JT8D was already obsolete, with the first small-to-midsize-narrowbody-sized high-bypass turbofans having entered service in the first half of the 1980s, simultaneously offering greater fuel efficiency and lesser noise than the old, outdated JT8D. Yet, despite this, the DC-9-80 only got more successful as the 1980s wore on and rolled over into the 1990s, with the single best year being 1991, and the years from 1987 through 1992 accounting for over half of all DC-9-80s produced.

Why and how was the DC-9-80 able to be so successful in the late 1980s and onwards, despite its 1960s-era engines rendering it obsolete just a few years after it entered service?

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    $\begingroup$ Obsolete? That word, I do not think it means what you think it means. $\endgroup$ – GdD Nov 8 '19 at 10:27
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    $\begingroup$ Why call it a DC-9-80 when most people know it as an MD-80? $\endgroup$ – JPhi1618 Nov 8 '19 at 15:40
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    $\begingroup$ Depends on your point of view : When I first traveled in an MD 80, I wondered why it looked so much like a DC-9. $\endgroup$ – blacksmith37 Nov 9 '19 at 18:27
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    $\begingroup$ @blacksmith37: That's because it is a DC-9. $\endgroup$ – Sean Nov 9 '19 at 22:22
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    $\begingroup$ -1 for the rollback. While you are right that it is a DC-9, nobody calls it like that. The aircraft is known as MD-80 or Super 80 series, so why remove the MD-80 from the question? $\endgroup$ – Bianfable Nov 12 '19 at 9:09

It's simple. Cheap (development costs amortized decades before) and reliable. They made money for airlines. Or, you know, they wouldn't have bought them. There's more to operating costs than fuel burn, and in any case, fuel prices in the mid 90s were cheaper than at any time since the 20s in constant dollars. Fuel was so cheap that Air Canada was bringing L1011s out of mothballs in the mid 90s because they could operate them Toronto to LA profitably.

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    $\begingroup$ How do you get the mothball smell out of something as big as an L-1011??? ;) $\endgroup$ – FreeMan Nov 8 '19 at 15:59
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    $\begingroup$ A bigger question is how do you get their little legs apart in the first place? $\endgroup$ – John K Nov 8 '19 at 17:15
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    $\begingroup$ 'because they could operate them profitably' +1. "obsolete" "efficiency" ... those words take a back seat to the Return on Investment. But there might be a slight inconvenience as you will be riding on a cargo plane full of live poultry. $\endgroup$ – Mazura Nov 9 '19 at 3:08
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    $\begingroup$ @Mazura - With the mothballs you won't smell the poultry. $\endgroup$ – Hot Licks Nov 10 '19 at 14:20
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    $\begingroup$ @FreeMan just open the windows and fly for a while $\endgroup$ – IMil Nov 11 '19 at 0:46

First, the airframe and systems were well-engineered and had few flaws and good aerodynamic qualities. Second, the cost to re-engine it with higher bypass ratio engines would have been high, and as such needed to be included in the cost-benefit analysis and balanced against the costs of operating the plane as-is with its original engines. The expected operational lifetime of the airframe would also enter into the analysis in the sense that if a re-engine exercise wouldn't break even before the airframe fatigue lifetime was exceeded, then the plane would be allowed to fly on into oblivion with its original engines and no one would care.

Bear in mind that the opposite is also true- that all the airplanes that used a geared 430 cubic inch 6-cylinder engine (with a 1100 hour TBO) like the twin bonanza, the aero commander 680 variants and various Cessna twins, would get abandoned when the engines were timed-out because the cost of annualing the airframe, rebuilding the engines, the props, and updating the avionics exceeded the value of plane in flying condition.

  • $\begingroup$ Even the very oldest DC-9-80s were no more than six years old by 1985 (practically brand-new by airliner standards), with many decades remaining in their airframe lifespans, and McDonnell Douglas did produce a reengined (and slightly stretched) version of the DC-9-80 a few years later. $\endgroup$ – Sean Nov 8 '19 at 2:20
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    $\begingroup$ @Sean economics. If it wasn't economically viable for the airlines to pay for the engine upgrade, then MD would have sunk the development cost for no return. When an airline was buying the MD-90, they were buying a bigger plane with a "full" lifetime, more efficient engines and no need to re-engine in the foreseeable future, therefore a different economic proposition. $\endgroup$ – FreeMan Nov 8 '19 at 16:02
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    $\begingroup$ @FreeMan I think your missing the point, which is that the question isn't about retrofitting existing planes with new engines at all. It's about why they kept making so many new planes with those old-design engines for so long, and in such numbers, after the better engines became available, instead of switching over much earlier than they did to having all the newly-made ones be made with the new engine designs. $\endgroup$ – Matthew Najmon Nov 11 '19 at 0:10
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    $\begingroup$ @MatthewNajmon the point still stands. It costs money to reengine an aircraft, whether it's on the flight line or still in the factory. MD would have had to invest money to change the MD-80 to fly with a new engine, and, odds are that they didn't feel it was worth the investment since the MD-90 was rolling out with a newer engine and more seats. $\endgroup$ – FreeMan Nov 11 '19 at 16:21

The MD80 was not obsolete at the time of its first flight and the decade thereafter. The market situation for 150 pax aeroplanes around 1980:

  • Boeing B727-200: first flight 1967. Three JT8D-7/9/11 engines.
  • MD-80: first flight 1979. Two JT8D-200 engines.

The first generation of JT8D had a bypass ratio of 0.7, the JT8D-200 engines had an increased bypass ratio. From the JT8D wiki page:

Designed to be quieter, cleaner, more efficient, yet more powerful than earlier models, the -200 Series power-plant was re-engineered with a significantly higher bypass ratio (1.74 to 1)

The MD-80 was a market leader and innovator, and was the best proposition 150-seat aeroplane for the airlines at the time. Two engines are more economical than three, higher bypass is more economical than lower bypass. Boeings response in the form of the B737-400 had its first flight only 5 years later, in 1984. The original B737-200 was smaller, made for 100 passengers.

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    $\begingroup$ The 737 Classic was officially launched in July 1980 (development having begun the previous year), saw its first orders in March 1981, first flew in February 1984, and entered service in November 1984. Although Airbus had been doing some conceptual design work on what would eventually become the A320 since 1977, the A320's first orders were in October 1983, it was not launched until a week after the 737 Classic's maiden flight, and the first A320 flew in February 1987, with entry into service only occurring in April 1988. The A320 most certainly did not spark the 737 Classic's development. $\endgroup$ – Sean Nov 9 '19 at 22:31
  • $\begingroup$ Your question is based on an incorrect assumption. $\endgroup$ – Koyovis Nov 11 '19 at 1:12

There's also benefit to parts commonality between aircraft, where if all of the DC-9 variants that an airline was flying were using JT8D engines, then that's one less airframe difference to be concerned about when it comes to maintenance and parts supplies.


Regarding the aspect of obsolence: in contemporary personal land transport, the Otto engine is, by pretty much all means, obsolete. There are very few cases in which the Otto engine outperforms an all-electric drivetrain, but these cases hardly make up more than 10% of the field.


The Otto engine prevails. Why? The infrastructure is there. The technology is tried and tested. Yes, you know its crap and that it will mess up the ecosystem of the generations to come, but you don't care, because in your broader perspective of economical and comfort-of-use reasons, it makes sense.

As a reference, you may consider what happened to Boeing when they tried to extend the lifespan of an archaic design while keeping it competetive. I'm guessing that's really the sentence in an answer you were fishing for ;)

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    $\begingroup$ And plants love the "fertilizer" CO2, NOx, and SOx, that Ottos spew. But efforts to monitor climate effects since the (colder than normal) 1970s are lauded. $\endgroup$ – Robert DiGiovanni Nov 9 '19 at 18:18

Also define obsolete. The 737, one of the (if not The) most successful airliner in the world was designed about the same time (1960s) and it shows no sign of seeing its production being stopped.

About narrow body = obsolete, I think you will find members of the CRJ (four-across seating [1]) and ERJ families that are not only are narrowbodies but look very similar to a DC9 (five-across seating) down to seat capacity.

About instrumentation on those aircrafts = obsolete, they are upgraded to stay compliant with new FCC regulations. And you will find airliners of the same vintage still flying today.

As others mentioned, there is the operational cost. At a given point in time (so the ratio between them is what we care) it cost 7.2 cents per passenger in operating costs to fly 1 mile on a 100-seat DC9-30 compared to 6.5 cents flying 108-seat Boeing 737-500s. [2] The cost per hour of the DC9-30 is 2053 US dollars[3] which is in the range for the CRJ1000 [1] (1700-2300), a plane launched in 2007 [4].

Finally, would you consider the Boeing 717 [5], i.e. the upgraded DC-9, obsolete?






  • $\begingroup$ The obsolete part I was talking about is the wasteful low-bypass engines, not the instrumentation or the narrowbody cabin. $\endgroup$ – Sean Nov 11 '19 at 1:52
  • $\begingroup$ The JT8D-9 was replaced with the JT8D-200 when it became the MD-80 and then the Rolls-Royce BR700 after it became the Boeing 717. $\endgroup$ – raubvogel Nov 11 '19 at 20:52
  • $\begingroup$ Even the JT8D-200, while a considerable improvement upon the earlier versions of the JT8D, is still a loud, fuel-hungry low-bypass engine. The DC-9 versions after the -80, which did (as you point out) switch to high-bypass engines, are not the focus of this question. $\endgroup$ – Sean Nov 15 '19 at 1:25
  • $\begingroup$ However, even with its (your own words) loud, fuel-hungry low-bypass engine, the cost per hour of the DC9-30 is comparable to a plane launched in 2007 aimed at the same market. $\endgroup$ – raubvogel Nov 15 '19 at 13:02

Why wouldn't an airline choose the MD-90, which was more efficient?

Airliners are usually retired because the airframe reaches the end of its useful life, not because the engines are "obsolete." Towards the end of an airliner's production run, the manufacturing process has been optimized and the cost to the manufacturer is lowest. They are willing to give good deals to customers to keep the money rolling in from that product line. It may be desirable for an airline to get a lower upfront cost on an airplane in return for higher running costs on less efficient engines.

As an example, TWA was able to order 24 MD-83s in 1998 and take delivery the next year. Boeing, who had acquired McDonnell Douglas by that time, got more orders to extend production, and TWA (who was in financial trouble at the time) got what was probably a great deal on brand new aircraft on short notice.

Why wouldn't an airline choose another company's options like the Boeing 737-400 or Airbus A320?

Brand and type loyalty is another important factor. Many airlines fly aircraft from a single manufacturer or even type because it reduces the cost of supporting many configurations for training and maintenance.

Not only was the MD-80 series delivered through 1999, but there are still many of them flying to this day, with operators like American Airlines only recently retiring their remaining fleet. They were worth ordering right through the 1990s because they were worth operating well into the 2000s.

The cargo market is much more tolerant of older and less efficient aircraft, but there are still 727s and 737-200s in revenue service, and the 767 is still getting orders despite passenger airlines switching to the 787 years ago.


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