Finding Normal

Engineering

Eddie sez:

What is normal and why is that important? Especially in the context of an airplane?

When you are flying it pays to know what normal behavior is so as to detect abnormal behavior. When you are troubleshooting a system you need to know what is normal as opposed to what the manufacturer considers within tolerances. Why? Read on.

In my first Gulfstream, and Air Force GIII, before the days of cell phones and before we carried cameras routinely, we once had an undocumented message on the first glass display ever used in a Gulfstream. Collins told us it was impossible and refused to entertain our complaint. Years later, as I will go into shortly, we had a right landing gear that seemed to take way too long to retract. How long? A few seconds. Gulfstream said that was perfectly normal. I dug through some videos and found evidence that something had changed. A few seconds may have been within tolerances but it showed that something had changed. We agreed to pay for them to investigate and they found a bushing on one of the sequencing arms of the right, inboard gear door worn beyond tolerances. The airplane was still under warranty so they had to pay for the time and replace the parts.

So perhaps all we did was save some money. But I think the worn bushing could have come to the point where it prevented the gear from extending and perhaps what we did was save us an inflight emergency. Either way, knowing what is and isn't normal came in handy.

So I continue to catalog normal. If you fly a G450 this can help you when looking for normalcy. Even if you don't fly a G450, this can show you a few tricks on how to begin your own catalog of normal.

Last revision:

20170601

Finding Normal

The Case of the Slow Right Gear

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Photo: G450 landing gear, from Eddie's aircraft.

The Complaint: The Right Landing Gear Extends Too Slowly

A few years ago we noticed it took longer for the right landing gear to extend and retract, just a fraction of a second. So we started watching it. After watching it for a few weeks the delay grew. On retraction, it could be as much as a second. On extension, as much as two seconds. We called Gulfstream Technical Operations who said as long as the entire operation took less than 3 or 4 seconds, we were okay. Good to go. Nothing to see here.

But wait, I said. If they were matched before and aren't now, isn't that a sign something in the system has gotten worse.

Nope. Nothing to see here.

Video Proof

So we took a view of the retraction on the landing gear synoptic:

G450 Landing Gear Retraction Problem (on synoptic)

The video clearly shows there is a delay, but not the total magnitude of the delay. Gulfstream was unimpressed.

Normal Gear Retraction

So I dug through the archives and found one of our gear retraction back in normal times:

G450 Aft Camera View Takeoff

So the right gear takes just a fraction of a second longer, even under normal operations. But our new delay was longer. Gulfstream came up with an explanation.

Gulfstream's First Excuse: Hydraulics

They said our left hydraulic system must be weak and because the right landing gear is further away from the left engine driven pump, the slow extension only makes sense. But we happened to know what normal hydraulics look like, and ours were normal:

G450 Hydraulics Synoptics During Gear Retraction

Gulfstream refused to entertain that we had a problem.

On Jacks, Proof

So we brought the airplane in, on our dime, and had them do a gear swing:

G450 Gear Swing (bad right gear)

Everyone within view said the samething: "That ain't right." So Gulfstream agreed we had a problem. since the airplane was still under warranty they paid for it too. Result: it was a worn bushing on a "timer valve" attached to the right inboard landing gear door. They replaced that and everything is back to normal.

The Case of the Bad DU

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Photo: G450 electrical panel during APU start, from Eddie's aircraft.

When we first got the airplane DUs 1 and 4 didn't always come up on battery power. Gulfstream thought of every possible excuse to say it was normal. That is until we pointed out the DUs had to be available down to batteries or the airplane could not have been certified. Our aircraft was no longer airworthy. So then began the chase for a solution. They claimed our batteries were underpowered. Fortunately we had a video showing how normal batteries behave:

G450 APU Start Electrical Panel

So it was back to the drawing board. They did, eventually, find the problem: a cut wire to a SGIO in the LEER.

The Case of the G450 Flap System (not normal on a good day)

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Photo: G450 flaps, from Eddie's aircraft.

If you fly a G450 you have to know about normal flaps because everyone at Gulfstream Technical Operations understand GIV flaps (easy), GV flaps (easy), and G550 flaps (just like the GV). But nobody knows what's going on with the G450. So my advice to you is to only move the flaps if you have AC power, never remove hydraulic pressure from any system unless the flaps have reached agreement with the flap handle, and to have an idea what normal is:

G450 Flaps Up / Flaps Down

The Case of the Sticking Intertank Valve

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Photo: G450 fuel system "slower" intertank valve, from Eddie's aircraft.

They teach you in school to check the intertank and crossflow valves together because "they are the same mechanical valve and should move at exactly the same rate." We don't do that because our aircraft is normally parked at a slight slope and this method will lead to a fuel imbalance. But do the valves move with equal speed? Ours do not:

G450 Fuel System Panel

The Case of the Disappearing Hydraulic Quantity

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Photo: G450 hydraulics synoptics from Eddie's aircraft.

After a few years of opertions we became used to the hydraulic system reservoirs never changing. (We check the synoptics before engine start, once we level off, during hourly checks, and after gear extension.) But all of a sudden we were losing a noticeable amount of fluid in the left seat sometime between engine start and level off. As the flight progressed, the quantity eventually came back. You can guess the answer to the inevitable question: "This is normal, you just never noticed it before. Luckily, we had video:

G450 Hydraulics Synoptics During Engine Start

So the investigation continued. As it turns out the hydraulic system reservoir bleed procedure is different in the G450 than the GIV. So if your mechanic came from a GIV where the bleed procedure was perfectly okay with the gear doors open you would end up with this characteristic. But if you follow the G450 maintenance manual and do the bleed procedure with the landing gear doors closed.

The Case of the Pressure Bumps

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Photo: G450 pressure bumps, from Eddie's aircraft.

After a few years of perfectly smooth pressurization we started experiencing pressurization bumps that were not associated with engine thrust changes, altitude changes, or any other noticeable change. Long distance troubleshooting didn't help. A video convinced Gulfstream we had a problem:

G450 Pressure Bumps

It turns out our TROV motor had gone bad.


How did I get those shots?

Hey, Eddie! How did you take those videos? Did you really put a GoPro on the bottom of the airplane?

No, not at all. The gear and tail shots all come from the manufacturer installed cameras. I simply strapped a camcorder on the forward divan, anchored with the seatbelts.

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Photo: Airshow Camera, from Eddie's aircraft.

So that's what gives you the aft camera shot on the top of this page, as well as this:

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Photo: Airshow Tail Camera, from Eddie's aircraft.

What about those shots looking forward from glareshield? I cut a plastic block with a 15° angle, put some Velcro on that, and used a Sony Bloggie camera. The setup is very secure and is below the pilot's eye level. The camera produces 1920x1080p at 30 fps.

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Photo: Glareshield Camera, from Eddie's aircraft.

What about the DU shots? I put a GoPro on a metal stick with Velcro on both sides. That setup wedges securely into the existing carpet like cover by the copilot's knee.

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Photo: DU Camera, from Eddie's aircraft.