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Today, commercial aircraft cockpit is manned by 2 pilots, previously it was 3 to 5. Is safety compromised in any way?

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    $\begingroup$ It depends on what kind flight you are actually talking about. Most domestic and close-proximity international flights usually have only 2 pilots while international flights have quite a few pilots. $\endgroup$ – SMS von der Tann May 15 '16 at 15:36
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    $\begingroup$ @SMSvonderTann Let's be careful. The cockpit is still manned by 2 pilots. I doubt that the OP is asking about relief and safety crew. $\endgroup$ – Simon May 15 '16 at 16:10
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    $\begingroup$ Actually there are less accidents with the computers and the FADEC doing the job of the navigator/flight engineer. Today's radio equipments are not comparable with old times. Some think that more automation is key to safety and this is likely true IMHO, at the cost of unrecoverable failures from time to time. Read this article in Vanity Fair. $\endgroup$ – mins May 15 '16 at 20:24
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    $\begingroup$ One might say that having the tasks divided up by too many cockpit crew is worse. That was a factor in the Charkhi Dadri mid-air collision where the ATC clearance did not make it from the radio operator to the captain in the 5-man crew. $\endgroup$ – TomMcW May 15 '16 at 21:12
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    $\begingroup$ If it did have a negative impact - wouldn't these supporting crew have been restored on most flights by now? $\endgroup$ – user1804 May 16 '16 at 1:10
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No aircraft ever had more than two pilots (on duty at the same time).

The additional flight crew members were flight engineer, navigator and radio operator.

  • Dedicated radio operators were only needed in the early days when the radio was primitive and required some care and experience to tune properly. As it improved, operating radio was merged into navigator or flight engineer job and eventually became simple enough for pilots to do themselves.
  • Navigators were used on long-distance flights especially over water. They kept track of the progress on the map and corrected the position using celestial navigation and some landmarks where available. With advent of inertial navigation systems and long range radio this simplified enough that dedicated crew member was not needed any more.
  • Flight engineer was most common and remained longest. Engines had many gauges that needed monitoring and controls that had to be correctly set to start them and adjusted to keep them running efficiently. And while turbine engines are simpler to manage than piston ones, the addition of more electric and hydraulic system meant that there was still a lot to set up and monitor. But now this job is done by a computer that monitors all the parameters and displays specific messages when something fails including instructions what needs to be checked and done for each problem.

In the meantime, the improvements in autoflight systems freed more time for the pilots in which they can now handle, with help of the electronics, the tasks that before needed a dedicated crew member.

Due to these technological advances allowing for the removal of these crew members, overall flight safety has not been compromised. It is likely that safety has actually improved by reducing the probability of human error.

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    $\begingroup$ On certain specialized planes, there might be a requirement for extra crew members. For example, some aerial refueling planes actually have a 3rd person who is called a pilot - but they don't fly the plane. They fly the refueling boom at the back, which has operates semi-independently from the aircraft itself. Not sure how many other examples like this exist, but that's one that I know about. (N.B.: I'm no pilot, but did work on a simulation of said aircraft, so my knowledge is a bit limited.) $\endgroup$ – Darrel Hoffman May 15 '16 at 18:08
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    $\begingroup$ @DarrelHoffman, I don't think the boom pilot would even count in the “flight crew” though. They also don't even work from cockpit. $\endgroup$ – Jan Hudec May 15 '16 at 20:50
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    $\begingroup$ Aren't they called "boom operators"? Here's another one, that is actually relevant for flight safety: the loadmaster on a cargo plane. He is responsible for pretty much everything related to the cargo; if you wanted to summarize his responsibilities in one word, it would be "center of gravity". Planes that operate on airstrips with limited infrastructure may have a flight mechanic on board (plus tools and replacement parts) who can fix problems without access to a maintenance crew / hangar. $\endgroup$ – Jörg W Mittag May 16 '16 at 1:50
  • $\begingroup$ @JörgWMittag - I've seen both terms used in official Air Force documentation, so it's not consistent. (Some of those documents may have been outdated, not sure.) @ JanHudec, true, they obviously operate at the other end of the plane. Not sure that disqualifies them as "flight crew" however. I believe they are also capable of flying the plane if the pilot and/or copilot are incapacitated at least. $\endgroup$ – Darrel Hoffman May 16 '16 at 13:37
  • $\begingroup$ @DarrelHoffman, there are many people on a typical aircraft that are “crew”, but not “flight crew”. “flight crew” is just those necessary to make the plane fly and the boom operator is not needed for that (a tanker might also be used as transport and then it will not have boom operator on board; it will probably have a load master, who will be “required crew member”, but won't be “flight crew” member either). $\endgroup$ – Jan Hudec May 16 '16 at 14:08
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Back before satellite navigation, affordable inertial navigation systems and small digital computers people had to do the tasks which are now automated. Navigation on long overwater flights was done by sextant, engines were managed by a flight engineer, etc. More people were needed because the jobs could not be done in any other way

Nowadays computers very efficiently handle many of the tedious and complex tasks, so there simply is not a need for additional cockpit crew. As for whether safety is compromised I would suggest you look at the accident rate over time as it's much lower than it used to be. As for how much of that is due to better automation in the cockpit I cannot say, but it certainly has not increased the accident rate.

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Your question seems to imply that having an extra hand on deck would help prevent an accident, which is not always true. Firstly, let's make a historical note that you're far from the first one to ask this question. When the DC-9-80 was being certified there was a heated debate between pilot unions and manufacturers over whether the two pilot crew was sufficiently safe, and a presidential commission tasked to investigate in 1981 concluded that:

The safety record of aircraft flown by crews of two is at least as good as the safety record of aircraft flown by crews of three. In our judgment, the presence of a third crew member in the DC-9-80 would not improve the ability of the crew to operate the aircraft safely in the air traffic environment. Therefore, safety-related improvements must come from measures other than enlarging the size of the flight crew.

The other answers have focused on decreased necessity of an extra crew member for navigation, engine tuning, and radio usage. I'd like to explain in the rest of my answer why having an extra crew member doesn't always prevent mistakes from a crew resource management (CRM) perspective. Occasionally in practice the extra crew member made the plane less safe.

CRM developed after some major cases where the flight engineer was ignored by the pilots and a crash resulted. In these cases the flight engineer certainly didn't prevent the accident. After all, when EAL Flight 401 descended too close to the ground the flight engineer wasn't even in the cockpit to monitor the low altitude alarm that sounded from his station. In my opinion the flight engineer's presence potentially makes it easier for the pilot to ignore warning signs that are the flight engineer's responsibility.

UA 173, one of the pivotal crashes for CRM, happened during approach when a problem with landing gear extension left the landing gear down and locked, but damaged the landing gear sensor assembly so that the landing gear indicator light did not come on. The pilots focused on this issue, and ignored the rapidly dwindling fuel supply. The flight engineer gave repeated hints about the fuel problem but the pilot ignored him. The NTSB said the pilot failed to monitor the fuel supply and did not take the flight engineer's comments seriously, and the flight engineer was not assertive enough.

The infamous Tenerife airport disaster happened when a pilot mistakenly thought he had takeoff clearance in low visibility and collided with a Pan-Am 747 that was still taxiing. The flight engineer of the taking-off plane had asked "Is he not clear, that Pan-American?" to which the pilot simply responded "Oh yes". The breakdown in CRM prevented the flight engineer from stopping the crash.

Accidents in which a flight engineer caused or failed to prevent an accident have greatly been mitigated by the improvements in CRM, but they still happen. In 2011, RusAir Flight 9605 crashed after the navigator had been giving mistaken directions and was even intoxicated, but the pilot did not question his guidance. Once again, the flight engineer may have made it easier for the pilot to ignore warning signs due to a breakdown in effective CRM. This was a similar situation to the 1996 Charkhi Dadri mid-air collision that TomMcW pointed out.

The President's Task Force on Aircraft Crew Complement similarly concluded that:

there is no advantage to any particular crew size in relation to safe and effective cockpit resource management. We also interpret incident, accident, and relevant research data to indicate that it is more difficult to achieve effective crew integration with larger crews. Distractions... should be dealt with by instituting more effective operational controls rather than by using a larger operating crew.

In summary, having an extra set of hands in the cockpit only helps safety when the crew is communicating effectively and using proper CRM. Quite a few flight engineers have failed to prevent or have even caused a crash.

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    $\begingroup$ You might also mention Germanwings 9525. The deliberate crash was facilitated by the fact that there wasn't a third crew member. $\endgroup$ – Kevin Krumwiede May 16 '16 at 21:50
  • $\begingroup$ My question focuses on times when a flight engineer clearly didn't help in a crash, so I'm not sure what would be the best place to stick in a flight where a flight engineer could have prevented the crash. $\endgroup$ – Cody P May 16 '16 at 23:20
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    $\begingroup$ @KevinKrumwiede Any third authorized individual, such that there were at every moment at least two people in the cockpit, would seem to have had the same effect on the events of Germanwings 9525. A flight attendant (who is certainly not flight crew), given some very basic training ("here is the cockpit door lock release, do X to it to open the door or Y to keep it locked, don't touch anything else unless instructed"), would have had the same effective ability to affect the outcome as a third fully trained pilot in the flight crew and would already have been on the plane for other reasons. $\endgroup$ – a CVn May 17 '16 at 6:39
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    $\begingroup$ Isn't this a correlation, rather than a causation? The era when there were routinely three or more people in the cockpit was also the era when cockpit crews didn't communicate effectively. It seems that the development of modern CRM techniques would make a three-person cockpit today much more effective at accident prevention than it was thirty years ago. $\endgroup$ – David Richerby May 17 '16 at 17:32
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    $\begingroup$ CRM is key; +1. Thinking back on a day when our flight engineer almost killed us; I can see - as with ocean-going and star ships - a captain not actively steering the ship can better assess, process, and act. But we don't have a captain + pilots. Nonetheless an aircraft captain can do precisely that with good flight crew management. $\endgroup$ – radarbob Sep 8 '16 at 21:11

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