Why isn't the arresting hook always used on land?

Danny Beckett
  • Why isn't the arresting hook always used on land? Danny Beckett

    Watching Jet Stream, about training to fly the CF-18 Hornet, they comment that the jet was originally certified as a Navy plane, landing on aircraft carriers with an arresting cable.

    Usually, when landing on land, they land hard and fast and take a mile of runway to come to a stop; but during an emergency, they use the tailhook which brings the jet to a stop after only 1,000ft.

    My question is: why don't they always use this to land?

    Here's a short clip I've taken from the show:

    • There is a lot of stress placed on the airframe when you use the tailhoook. You can see the skin buckling in the picture below behind the landing gear. I'll admit, you probably wouldn't land intentionally with this sort of technique on land but if you catch the wire during the flare it could probably pull you down pretty hard. For these types of landing and it would be difficult to get it right every time.

      (Like I wrote in the comments, I do realize that the aircraft below has not yet caught the cable. When you flare, and you might catch the cable mid-air if you have a nose-high attitude, and slam down hard as it pulls you backwards and you loose lift, or you do a non-flare like carrier pilots, also very hard. IMO I think either would end up like the landing below.) stress

    • You have no ability to control the aircraft and you end up stopping and rolling backwards on the runway. You can only be one aircraft at a time and you cannot roll off straight away, wasting time.
    • You'd have to have an arresting gear system and along with that more staff and maintenance.
    • At least on aircraft carriers, I believe the arresting cable has a limit of only 250 catches for safety reasons. Even if it the limit was greater on land, you'd have to have people changing the cables on a regular basis.
    • You'd still have to have conventional brakes which you could just as well use.

  • There are several reasons why arresting cables aren't used on land:

    Stress

    As Manfred noted, the stress that gets put onto a plane during landing is incredible. According to HowStuffWorks "How Aircraft Carriers Work", its not unusual for an aircraft to hit the deck at around 150 mps or about 67 mps. Since they have less than 500 feet of runway (~150 meters), they must decelerate at an incredible speed to a standstill in about 2 seconds. That equates to about 3.5 G's! In addition, Navy pilot's are taught to push the throttle to max upon hitting the deck so that if they miss one of the 4 cables, they can still have enough speed to take off and try again. This may now happen automatically as Chris S noted, I'm not certain. This means that the aircraft has to undergo even more stress. Navy planes must hit the deck so hard that its often compared to a controlled crash instead of landing and aircraft frames must be structurally modified to endure that type of stress.

    Difficulty

    According to Tom Clancy's, Carrier: A Guided tour of an Aircraft Carrier, it is extremely difficult to catch the wires. Its so difficult that Navy Pilots are often ranked on how often they hit the 2nd wire (considered to be the best).

    Price

    As Manfred noted above, the machinery to slow an aircraft is not trivial. While I'm not familiar of the routine replacement rate for these cables, I would imagine that it would be something else that would have to be monitored. The cable is actually attached to a large machine which provides the cable with some give. I can't imagine that they would be cheap, but I'm not familiar with the exact machinery myself.

  • Some military runways (on land) do have arresting cables. These are not intended for routine use, but to catch aircraft in danger of running off the end of the runway due to brake failure, touching down too late, etc. Sometimes they may pop-up to snare the undercarriage rather than using a hook, Navy style.

    The reasons for not using arresting cables on land have been well discussed above -- airframe and pilot stress from the high G's, maintenance costs, etc. Also, there's usually plenty of land on which to build a runway, so you don't need to stop short as on a carrier.

Related questions and answers
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