What an awful choice of terminology though - it’s almost designed to be confusing to anyone outside the space.
1,425 karma · joined August 8, 2014
"Pretend you're an experienced support engineer talking to a pilot flying an F-35. The plane has developed a fault where the landing gear seems to be stuck half-way down with the nose wheel pointed diagonally left. Aattempts to raise or lower the landing gear do not result in any motion. a single touch-and-go has been performed with no change in the situation. the weather is very cold currently, at -1F. Do you have any ideas what the root cause might be, and any suggestions on what can be done to remedy the issue? Think carefully and explain your reasoning for each step. Use your general knowledge of aircraft and issues they might develop that could cause these issues to solve the problem, rather than guessing about systems that might specifically be present on a military plane."
ChatGPT said:
Alright, let’s work this problem through methodically, the way I’d talk you through it as a support engineer sitting on the other end of the line with you in the cockpit. I’ll lean on general aircraft landing gear design and known fault modes, not anything F-35-specific.
1. Restating the situation
- Landing gear is stuck mid-extension.
- Nose wheel is cocked diagonally left.
- No further movement when commanded up or down.
- One touch-and-go performed — no improvement.
- Ambient temperature is very low (−1 °F / ~−18 °C).
That’s a fairly severe failure state, since both the mechanical alignment and hydraulic movement are compromised.
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2. Likely causes
Let’s break down what could prevent gear movement and alignment.
(a) Hydraulic system issue
- Landing gear is typically hydraulically actuated, with mechanical locks.
- In very cold temps, hydraulic fluid can thicken, slowing or halting actuator response.
- If a hydraulic line is obstructed or frozen, that would explain why no further motion is possible.
- A hydraulic control valve could be jammed halfway.
(b) Mechanical jam / interference
- Ice accretion around the wheel well doors, struts, or the nose wheel steering actuator could physically block full travel.
- Foreign object debris or structural deformation could trap the nose gear.
- Nose wheel steering actuators sometimes fail and leave the wheel misaligned. Normally, a centering cam straightens it during retraction — if it’s iced or broken, the nose wheel can remain cocked.
(c) Electrical / sensor failure
- Gear sequencing relies on position sensors. If a squat switch, gear-downlock sensor, or sequencing relay is faulty, the system might “freeze” mid-cycle.
- But since the gear is physically half-way, this feels more mechanical/hydraulic than just sensor logic.
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3. Why the nose wheel being cocked matters
Normally, when retracting, the nose wheel passes through a centering cam or is hydraulically straightened before stowage.
- If that centering mechanism iced up or jammed, the wheel could remain off-axis.
- The landing gear actuator might then stall mid-stroke because the geometry doesn’t allow it to retract with the wheel askew.
- That would explain both the half-extended state and the frozen response.
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4. Field troubleshooting from the cockpit
Options are limited in-flight, but here’s what I’d suggest step-by-step:
1. Recycle the gear: You’ve tried once already. Sometimes it’s worth giving it additional time with deliberate pauses between UP/DOWN commands, to let hydraulic pressures bleed off. But repeated cycling risks further jamming.
2. Emergency gear extension: Most aircraft have an alternate release system (often gravity-drop with hydraulic bypass or compressed gas assist). That bypasses sequencing valves and lets the gear fall into place. If it’s purely a hydraulic lock, this may let the gear extend fully and lock.
- If you haven’t already: consider attempting emergency extension.
3. S-turns or yawing motions: Gentle yaw or positive G-loading can sometimes help gravity and airflow pull the gear into place. Not aggressive, but enough to “jostle” the jammed mechanism.
4. Thermal factor: At −1 °F, icing and fluid thickening are prime suspects. Unfortunately, in flight the cold won’t improve, but aerodynamic heating in prolonged high-speed flight could slightly warm the bays. That might free up iced components — but it’s not guaranteed.
5. Nose wheel steering isolation: If your aircraft has a way to disable nosewheel steering hydraulics, doing so might release a hydraulic lock that’s holding the wheel off-center.
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5. Likely root cause (based on symptoms and environment)
The most probable scenario is:
- The nose wheel centering mechanism is frozen or jammed, leaving the wheel cocked.
- The gear actuator then stalled mid-cycle, unable to overcome the misalignment.
- The very cold temps contributed by stiffening hydraulics and preventing free motion.
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6. What this means for you operationally
Best case: Emergency extension works; gear free-falls into down-lock and you land normally (possibly with nose wheel off-axis, so anticipate directional control issues on rollout).
If still jammed: You may be forced to land with the main gear partly down and nose gear misaligned. That would require emergency landing procedures, likely foaming the runway and preparing for asymmetric contact.
Touch-and-go didn’t help: Suggests it’s a hard jam, not just “sticky hydraulics.”
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My recommendation:
Attempt emergency extension immediately.
If that fails, fly some time at higher speed to warm the bays, then retry.
Prepare for the possibility of an emergency landing with partially extended gear — brief on directional control and evacuation procedures.
Donut Media actually has a great video on the topic: https://www.youtube.com/watch?v=t58qjcNwEbo
As far as my understanding goes, it's basically a low-pass filter that also provides momentum in the direction of movement - this actively dampens spring oscillation (as opposed to a shock absorber, which passively dampens oscillation). It should be installed in parallel with the spring and shock.
A log entry should capture an event in time, for example: a person logging in, a failure, a record of a notable event occurring, etc. These should be written at the time they occur when possible, to minimise chance of loss and to minimise delay for any downstream systems that might consume the logs. Arguments for batching could easily be made for systems generating very high volumes of logs.
Conversely, a metric is a single value, point-in-time capture of the size of something, measured in units or with a dimension. For example: current queue depth, number of records processed per second, data transfer rate in MB/s, cpu consumption percentage, etc. These can/should be written periodically, as mentioned in TFA.
If you're unfamiliar with the phrase then it's likely meaningless, but if you do know then there's no chance of getting it incorrect.
Use depends on context, like all language, and deliberately choosing a situation that doesn't suit the language will obviously result in confusion.
Anything that's a word instead of a precise number implies a range to me (eg, few, handful, several).
It's more than several, but still a manageable number.
I use "<day> week" in conversation, but I'd say it's falling out of favour. I mostly use it with my parents.
"Next Friday" is always a week+ away. If it's Tuesday and I say "next Friday", I ALWAYS mean the day 10 days away.
If someone says "next Friday" to me and they mean the one in a few days I'll look at them like they're crazy.
several = 5-10
handful = 10-20
Personally, after having worked in a hardware store, I always confirm. "grab me a couple of those please" - "is two enough, or do you need a few extra?"
I'm one of those people for whom a couple is 3-5, but never 2. I would just say "two".
The most expensive RAV4 is around AUD$65,000, while the cheapest Telsa Model Y is around AUD$70,000.
HN is primarily a news site that allows discussions - I wouldn't classify it as social media. Heck, Reddit barely qualifies as social media for me.
My internal definition is probably two decades out of date, however.
I know the lane-keeping assist function in my 2024 car (that turns itself back on every time I start the car) has a healthy appetite for trying to veer the car into oncoming traffic whenever I’m on a road with no lane markings. This is quite common on suburban roads. So far I’ve been lucky, but if it happens at just the wrong moment I can absolutely see it causing a head-on collision that wouldn’t have happened otherwise.
For me this is the crux of the issue - these systems greatly improve some situations, but it’s not acceptable to do so at the expense of worsening others.