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To my knowledge, most aircraft with retractable gear are equipped with a landing gear warning system that makes repetitive beeping sounds in case the pilots try to land without the gear down.

I imagine big jetliners like Airbus and Boeing would have a far more advanced landing gear warning system, but does any of them have a landing gear system that extends automatically if the pilots fail to extend the gear and continue their descent for landing despite the warning?

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    $\begingroup$ As I remember, some models of the Piper Arrow and the Beech Sundowner had automatic landing gear extension, but I've never heard of such for large aircraft, and I don't recall any jetliner ever having made a belly landing because the the pilots forgot to extend the landing gear and ignored the warnings. $\endgroup$ – Terry Jul 25 '17 at 2:24
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    $\begingroup$ The danger introduced -- the system malfunctioning and extending unexpectedly inflight or extending during a ditching -- probably outweighs the danger mitigated -- pilots forgetting to extend the gear despite warnings. $\endgroup$ – Thomas Jul 25 '17 at 2:35
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    $\begingroup$ What if the pilot actually wants a belly landing, like in the Miracle On The Hudson? $\endgroup$ – Koyovis Jul 25 '17 at 4:48
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    $\begingroup$ @ Koyovis: And particularly for aircraft other than commercial airliners, how do you reliably detect that a landing is intended, rather than just a desire to fly low & slow? $\endgroup$ – jamesqf Jul 25 '17 at 6:28
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    $\begingroup$ The proper question that should be asked before is: how many instances were there that a big airliner landed with gears retracted because the pilots forgot to extend them? $\endgroup$ – PlasmaHH Jul 25 '17 at 11:30
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The simple fact is that an unintended gear deployment could be catastrophic, as it has a profound impact on the flight dynamics of the aircraft (one of the reasons there are warnings for both retraction and extension).

The benefits would be marginal as checking gear down is part of the bread-and-butter procedures for all retractable gear aircraft.

Keep in mind adding some automation to an aircraft has far ranging impact, just off the top of my head adding automatic gear mechanism would require:

  • Standardization of the automation
  • Modification of procedures
  • Training of pilots, and then re-certification of pilots
  • Training of maintenance crews, and then re-certification of the crews
  • Possible change to the maintenance schedule of aircraft
  • Certification of the new system by the regulator

and you would still need a backup / redundant system; and now you are back to the manual controls.

I can imagine this being implemented in remote piloted or autonomous aircraft though; as an additional workload relief.

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  • $\begingroup$ An autonomous aircraft with retractable gear that lands automatically would need to be able to handle this anyway and will already have it. Most likely some custom design. $\endgroup$ – BeowulfNode42 Jul 25 '17 at 8:19
  • $\begingroup$ Yes, but I was assuming remote piloted aircraft - not autonomous. $\endgroup$ – Burhan Khalid Jul 25 '17 at 8:22
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    $\begingroup$ Very good answer. I would add that in the event of a voluntary belly landing, it would be inappropriate to add workload into the cockpit just to prevent this "automatic landing extension" from occurring. $\endgroup$ – le_daim Jul 25 '17 at 10:19
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It has been tried before. Piper's PA-28R and PA-32R aircraft were equipped with an automatic landing gear extension system which would automatically extend the landing gear below 85kts regardless of the position of the selector switch in the cockpit. At higher airspeeds this system was overridden by a separate pneumatic system which deferred control to the cockpit selection handle.

This system did have its drawbacks, most notably being there are times where a pilot wishes to keep the gear retracted regardless of airspeed for performance reasons. A fatal crash involving a PA-28 caused by an increase in parasite drag from the gear automatically extending caused Piper to subsequently issue an AD requiring all PA-28s and PA-32s with the automatic gear extension systems to be fitted with an emergency override, allowing the pilot to continue to command the position of the gear with the cockpit selector handle regardless of airspeed.

I suspect most GA aircraft and transport category airplanes never implemented such a device because the risks of an inadvertent gear up landing were outweighed by the advantages of having the ability to select the position of the gear for operations in all areas of the flight envelope.

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  • $\begingroup$ While practicing stalls or slow flight an Arrow will drop the gear, unless you remember to hold the override in position. $\endgroup$ – Adam Jul 25 '17 at 13:06
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    $\begingroup$ Wow, so when landing (in a nice controlled fashion or otherwise) instead of the pilot choosing to lower the gear or not, the pilot can choose whether to: lower the gear, not lower the gear, allow the gear to lower on its own, not lower on its own but then lower it themselves, or not lower on its own but then continue to keep it up... Did I miss any? $\endgroup$ – Grimm The Opiner Jul 25 '17 at 15:01
  • $\begingroup$ The EMERG OVERRIDE lever has a manual locking pin on it which can be engage prior to flight. Usually it is left engaged as such per the OEM checklist unless needed for an emergency. $\endgroup$ – Carlo Felicione Jul 25 '17 at 17:02
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    $\begingroup$ If the pilot either forgets to command the gear down using the panel selector switch or willfully omits this task, once the airplane decelerates below 85kts, the gear will extend and the landing gear warning horn will activate, except if the throttle is wide open. Also during takeoff if the EMERG OVERRIDE is engaged and the pilot commands the landing gear up using the panel selector switch, the landing gear will not retract until the aircraft accelerates past 85kts or the EMERG OVERRIDE lever is pulled up and locked in place. $\endgroup$ – Carlo Felicione Jul 25 '17 at 17:20
  • $\begingroup$ My first night flight as a student was in a PA28, and the instructor neglected to tell me about that feature. We're climbing out, I'm utterly entranced with the moonlit night and... beep-beep-beep and the dash lights up - oh lord, something serious has broken. Nah, the instructor said, and pulled the override. From that, I learned two things: Know your aircraft before flying it, and carry extra underwear. $\endgroup$ – tj1000 Jul 27 '17 at 0:21
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Adding such automation is not what the manufacturers want to be doing.

  • It is additional work and costs money.
  • It is another system that might fail.
  • This is not a trivial matter. There are lots of variables to take into account. Complex rules would have to be made when to extend gears. For example when ditching in water we don't want gears to extend.
  • As the pilot may not be aware that the gears are retracted, now we have the possibility to not know that they are automatically extended.

Aircraft manufacturers would probably just issue a bulletin reminding pilots to operate the landing gear when needed. Accident investigators would probably want to eliminate the reason that lead to the omission of a checklist item (proper sleep etc.).

Sidetracking a bit, but sometimes automation fails:

  • When flying some Boeing aircraft, the pilot should be able to know that when some sensor reading are different between pilots' displays, the autopilot & autothrottle might get erroneous data and shouldn't be used. Planeloads of people have died because of pilots' inability to connect the discrepancy of sensor readings to the erratic behavior of the aircraft.
  • Meanwhile, an Airbus A330 flew into thunderstorm, had its pitot-tube frozen for a short duration, and after receiving conflicting information disengaged the autopilot. The pilots needed just to fly straight forward, but one of them panicked and stalled the aircraft, killing everyone onboard.
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