# What are the states that the landing gear can be in?

What are the valid set of enumerated states for landing gear?

My current working set is:

• DOWN
• DOWN & LOCKED
• STOWED
• STOWED & LOCKED
• INOPERATIVE
• CYCLING_UP
• CYCLING_DOWN

Also, are there any definitions in which UP is distinct from STOWED? (I can't find any.)

• What is the purpose? Aug 18, 2014 at 15:29
• Primarily seeking to clarify my understanding of all valid states. Aug 18, 2014 at 15:40
• Are you asking as a pilot or a programmer? I'm asking because it sounds kinda like you're trying to create a model of a plane Aug 18, 2014 at 15:53
• if you allow the bay doors to malfunction then you can have up/locked and not stowed Aug 18, 2014 at 16:06
• What exactly does INOPERATIVE mean? It seems like the landing gear could become inoperative at any point, and it's important to distinguish, say, landing gear that's down and locked but can't be moved from landing gear that's up and locked and stowed but can't be moved. Aug 18, 2014 at 16:12

Any instruments always show only three states:

• Down and locked (green)
• Up/stowed (extinguished)
• Anywhere in between (red)

If you want to simulate it, remember that while the pilot can only command one of the two end states, the transition is a continuous process and you need to represent exact position of the gear in each frame of the simulation. So you need a value that will smoothly transition between 0 (stowed) and 1 (down and locked). Any value in between will indicate red on the instrument, but will correspond to different state of the gear animation.

The exact steps during gear extension (and in reverse for raising) differ by aircraft, but generally the animation will have three parts that you will map to suitable ranges of the gear state value:

• opening the gear door,
• lowering the gear and
• closing the main gear door.

The last step actually complicates issues a bit, because the gear is already down and locked when the main gear door close and in case you do gravity extension the main gear door remain open.

So the suggested mapping is actually something like:

• opening the gear door 0.0 to 0.3
• lowering the gear 0.4 to 1.0
• closing the main gear door 1.1 to 1.4

When you extend the gear normally, the value will transition up to 1.4 (and show green past 1.0), when you extend the gear via alternate mechanism (gravity drop), it will only transition to 1.0. If you want to simulate alternate extension, of course.

Tweak the values to make the animation look appropriate. The relative speed differs by aircraft. Some aircraft also don't have gear door (e.g. 737 only has one panel that is attached to the strut on main wheels; it still does have nose gear door, so the process will be slightly different for each leg).

Which leads me to note, that if you want to simulate failures, you definitely need separate value for each leg, because some failures, like jammed actuator, only affect one gear. Also in reality the legs take slightly different time to extend, so you can add some variability to the transition time if you wish.

• Just a small note that bugs me every time: Red is not 'in between'. Red means 'gear position is not in agreement with lever position' Aug 18, 2014 at 19:27
• In addition, most gears do not move at a constant speed between up and down, but move faster when gravity supports the motion. Also, to minimize the demands on the hydraulic system, the left and right main gear on many planes do not move in sync, but with a notable time difference. Aug 18, 2014 at 19:54
• @Radu094 The meaning of red varies with the aircraft. In my airplane, for the main gear it simply means that the gear doors are not closed and has nothing to do with the gear itself. For the nose gear, since it doesn't have a gear door that closes, it means that it is in transit. Aug 19, 2014 at 3:58
• @JanHudec When we gravity extend (our second alternate extension method) we will have three green and two red lights. The nose gear red light will be the only one that goes out, since it doesn't have a door that is supposed to close. Aug 19, 2014 at 8:12
• @Radu094 In our case, We would get no red or green lights for the mains, but a flashing red gear handle as a warning (that warning is a disagreement light) as well as the gear warning horn under the appropriate conditions (full flaps selected, etc.). Aug 19, 2014 at 8:16

To give an idea of the states that are possible along with the indications (and generally the complexity of the system) here are some tables from a 767-300.

• Excellent, information. This is certainly a great insight as to how this has been implemented and is being used in the industry. Jul 8, 2015 at 16:47