Not Your Father's Gulfstream
Many of us longtime Gulfstream drivers are fond of saying, "She's built like a tank!" Or, "the Gulfstream flies conventionally." In fact, I am guilty of saying these things on many of these pages. And that is, for the most part, true. But the G450 is an exception.
If you've grown up in anything older than the GV, thinking this aircraft flies like any other can bite you. Even if this is your first Gulfstream, you need to understand that the G450 is unique and has many unsavory traits that require you to rethink what you know about airplanes.
- The Landing Gear Selector Valve on the GV series (including the G450) is not mechanically connected to the landing gear handle. This can have a major impact on how you treat landing gear issues.
- The Flaps on the G450 are a Frankenstein creation blending the GIV and the GV and coming up with something worse than both. Think you can operate the flaps without AC power? You probably can't. Think you have back up flaps? You don't.
- The Ground Spoilers on just about every Gulfstream since the GII can bite you, but a misunderstanding of the added "combined" weight on wheels system can give you a false sense of confidence in them. The ground spoilers can be deadly with or without the combined WOW and should impact the way you handle the throttles after takeoff and before landing.
- The Avionics of every Gulfstream up to an including the GV were pretty bullet proof and problems easily diagnosed. With just a basic understanding of electrons you could get yourself a flyable airplane without too much drama. That ended with the G550 and can be even worse in the G450.
- Gulfstream Support went from fair (circa GIII and before), to very good indeed (circa GIV and GV), to fantastic (G550), to fair again for one particular aircraft, the G450. We are already a "legacy" aircraft and, worse than that, we are relegated to the second team. Why is that? How do you cope?
Photo: G450 N667HS, Salzburg (LOWS), 11 Apr 2017 (Photographer: Roland Winkler)
Landing Gear Selector Valve
The saying goes, "there are those who have and those who will forget to pull the landing gear pins prior to takeoff." I don't believe that, but imagine if it did I would be a bit upset. In a "conventional" airplane you would be tempted to land, pull the pins, and takeoff again to minimize the embarrassment. In any GV series aircraft, including the G450, I would be inclined to land, put the aircraft on jacks, and cycle the gear a few times just to be sure. Why such paranoia? Read on . . .
For as long as I've been flying GV series aircraft, we have been told that if we raise the gear handle with the pins installed, we need to press and hold the landing gear dump valve switch for three seconds in order to have normal anti-skid braking. It was implied that at this point, we had a normal airplane again. There have been several instances where the brakes locked up after landing that seemed to validate this fear. But sometimes braking was normal. Everyone seemed to focus on the need to do this for braking and braking alone. I too ignored the evidence that is written, albeit written poorly, in the note on the procedure itself:
[G450 QRH, pg. EC-19] NOTE: Selection of the DUMP switch will not affect the dump system or illuminate the switch capsule, but will provide an alternate electrical ground path for energizing the normal landing gear extend solenoid. This will return the landing gear system to the normal landing gear extended configuration for landing.
In other words, until you do that, the "landing gear system" may not be in the "normal landing gear extended configuration." Quite a bombshell, that. But to understand why, let's look at the GIV landing gear selector valve first.
Figure: GIV Landing Gear Lever Linkage, from GIV AOM, §2A-32-00, figure 7.
The landing gear handle on the GIV (and most "conventional" airplanes) has a direct, mechanical, linkage to the landing gear selector valve. In other words, if the gear handle is up, you can be certain that if any hydraulic pressure is being directed to the gear, it will be directed in the retraction direction. Conversely, if the gear handle is down, you can be certain that if any hydraulic pressure is being directed to the gear, it will be directed in the extension direction.
But that is for a "conventional" aircraft. What about the G450?
Photo: G450 N667HS, Salzburg (LOWS), 11 Apr 2017 (Photographer: Roland Winkler)
On April 11, 2017, Gulfstream G450 N6667HS returned to land at Salzburg Airport (LOWS) after declaring a PAN. After landing one pilot went to inspect the landing gear on a remote taxiway, after which the nose landing gear collapsed. As of May 21, there still isn't any official comment from Gulfstream about this and the rumors are flying. Rather than add to the speculation, let's look at a few things that make the GV series aircraft susceptible to a nose gear collapse after raising the gear handle with the pins installed.
The Gear Handle is Not Mechanically Linked to the Landing Gear Selector Valve
[G450 AOM, §2A-32-10] Extension and retraction selections are made with the cockpit landing gear handle that electrically signals the solenoid on the landing gear selector/dump valve. The selector/dump valve directs hydraulic pressure in a defined sequence to open the gear doors, extend or retract the gear and close the doors when the gear have reached the selected position.
[G450 MM, § 32-30-03 ¶1.A.] The hydraulic control valve (selector / dump valve) contains two electrically controlled valves. The selector valve controls the normal landing gear extension and retraction. The dump valve controls the emergency extension.
[G450 MM, § 32-30-03 ¶3.A.] The selector valve portion of the control valve ports hydraulic fluid to raise and lower the landing gear by receiving electrical signals from the landing gear handle in the cockpit. The dump valve portion of the control valve is actuated into the emergency dump position by pneumatic pressure and is reset to the normal position by solenoid actuation.
This is just like the mechanical valve you had in the GIV, but instead of a cable from the gear handle to the valve you have electrons which move a solenoid. In earlier Gulfstreams the valve was underneath the cockpit and the hydraulic lines traveled aft. In the GV and later, the valve is in the wheel well.
When electrically activated by the cockpit landing gear handle, the landing gear hydraulic control valve sends hydraulic pressure to the landing gear door control valves to begin the extension or retraction sequence.
The landing gear handle in the cockpit is an electrical switch that asks the landing gear selector valve to move, retract when the handle is up, extend when the handle is down. Note that it "requests" the movement. If the system hasn't sequenced, the request can go unanswered. More about this: G450 Landing Gear Control.
The Landing Gear Selector Valve Remains in the "Retraction" position until Something Else Happens
[G450 MM, §32-00-00, ¶4.A.] When the landing gear handle is placed to the up position, the landing gear selector / dump valve is electrically energized, porting left hydraulic system pressure to the door control valves, uplock actuators and retract timers. The door control valves route pressure to the door actuators, opening the doors. When the doors are nearly open, a mechanical linkage actuates the retract timers, routing pressure to unlock the landing gear and pressurize the retract ports of the side brace actuator and the nose landing gear actuator.
Note that all this happens even with the pins installed. However, what follows may or may not happen because the first condition, the nose landing gear coming out of the over center condition, is prevented.
[G450 MM, §32-00-00, ¶4.A.]
- The nose landing gear downlock actuator forces the downlock linkage out of the over center condition, allowing the nose landing gear to move. The pressure to the side brace actuator is used to release the internal downlock, allowing the actuator to move. The nose landing gear and side brace actuators move the landing gear to the retracted position. The first upward movement of the landing gear repositions a linkage placing the door control valves in a neutral position. This prevents the flow of hydraulic fluid to either the door open or the door closed ports of the door actuators, preventing door operation. When the landing gear is almost fully retracted, the uplock hooks are activated by the uplock rollers and the uplock actuators are moved to the closed position. With the hooks fully closed, the door control valves are positioned to route pressure to the door closed port of the door actuators. This causes the landing gear doors to move to the closed position.
- After the landing gear has retracted, the landing gear components are positioned as follows:
- Nose landing gear and side brace actuators are unpressurized in the retracted position
- Doors are closed and locked with door actuators pressurized in the fully extended position
- Uplock actuator is pressurized in the retracted position
If we had left the pins in, the correct procedure is to press and hold the landing gear dump valve switch for three seconds:
Figure: G450 Attempted Gear Retraction With Pins Installed, from G450 QRH, pg. EG-19
Of course this implies the landing gear selector valve will be in the wrong position if you don't do this. Furthermore, it also implies that once you pull the pins the gear will retract if you have any hydraulic pressure on the system. It appears that in the case of N667HS the engines were shut down, the pilot removed the pins, and the aux pump was used to close the landing gear doors. We know we can use the aux pump to swing the gear if the airplane is on jacks. So if this theory is correct, why did only the nose gear retract?
The Main Gear Downlock System is Strong / The Nose Gear Downlock System is Weak
The main landing gear downlock system requires considerable hydraulic pressure to overcome:
[G450 AOM, § 2A-32-20 ¶2.C.(1)] The side brace hydraulic piston and actuator arm extends the main landing gear outboard and down from the wheel well and locks the landing gear in the down position using internal locking keys located in the lower end of actuator cylinder. The keys slide into annular slots when the side brace actuator reaches full extension. A lock ram positioned by down hydraulic pressure and a spring maintain the keys in the slots preventing any further actuator movement. Spring pressure is necessary to maintain the keys in the locked position without hydraulic pressure. The movement of the keys into the slots also provides the input for the downlock micro switch that provides the cockpit indication that the gear is down and locked. When the gear is selected up, hydraulic pressure is ported to the other side of the lock ram, displacing the keys from the slots and overriding spring pressure, allowing the actuator to move in the retract direction. The side brace actuators have provisions for inserting ground lock pins to maintain the main landing gear in the extended position during ground operations.
The downlock is inside the side brace actuator cylinder. In the down position, keys move to allow the downlock electrical signal and prevent strut compression. The keys are held in place by springs and can only be moved with hydraulic pressure. Theoretically, the main landing gear will not retract without a considerable amount of hydraulic pressure because most of the aircraft's weight is on the main gear. The nose gear, on the other hand, carries much less weight and relies on an over center brace:
[G450 AOM, § 2A-32-20 ¶2.C.(2)] The nose gear actuator pulls the nose gear aft and down to the extended position. One end of the actuator is attached to the aft structural wall of the nose wheel well. The other end is attached to the hinged nose gear trunnion that pivots aft into the extended position.
[G450 AOM, § 2A-32-20 ¶2.C.(3)] Nose gear downlock engagement is provided by the over center position of the hinged two part truss brace with integrated downlock actuator and spring. The forward and aft sections of the truss brace unfold as the nose gear extends. As the truss brace unfolds, it forces open the “C” shaped suitcase springs. When the nose gear is fully extended, a hydraulic downlock actuator and linkage pulls the truss brace slightly over center at the hinge point. The truss brace hinge is also held in the over center position by the energy of the “C” shaped suitcase springs that close slightly in the over center position. The springs are necessary to maintain the nose gear in the downlocked position without hydraulic pressure. Once locked into the over center position, hydraulic pressure on the retract side of the downlock actuator is required to push the truss brace past the over center position and overcome spring pressure. The truss brace hinge has a provision for inserting a down lock pin to secure the nose gear in the extended position.
[G450 AOM, § 2A-32-20 ¶2.C.(4)]The downlock micro switch on the nose gear is located on the truss brace. As the truss brace unfolds to the over center position the contact on the nose gear micro switch is depressed sending a downlocked signal to the landing gear control panel.
It takes hydraulic pressure to force the nose gear into the down position and the truss brace over center. Sitting on the ground without hydraulic pressure, only the "suitcase" spring ensures the truss brace continues to be over center It could easily move if jostled during towing, hence the need to insert the downlock pins whenever the airplane is towed. It is theoretically possible that the aux pump alone could overcome this suit case spring and retract the nose gear on the ground.
More about this: G450 Landing Gear Uplocks/Downlocks.
Following the Checklist is Key
It appears the pilots of N667HS did not complete the appropriate checklist and did not press and hold the landing gear dump valve switch for three seconds. A careful study of the only documented case of this happening before reveals something important:
- A G450 operator contacted Technical Operations with the following landing gear issue. After takeoff, the crew selected the landing gear handle to the up position, but all three landing gear failed to retract. The landing gear handle was free to move and was not impeded by the landing gear handle lock release button. It was also observed that the landing gear control circuit breaker was not extended or “popped.” All hydraulic systems were operating normally.
- At this point, the crew selected the landing gear handle down and elected to return to the departure airport, where they made an uneventful landing.
- After parking on the ramp, the crew discovered that all three landing gear actuator pins had been left installed. They also noted that the brakes seemed to be “dragging” considerably during taxi to the ramp.
- A review of the incident determined that the flight crew did not follow the landing gear failure to retract procedure. This procedure is located in the Quick Reference Handbook (QRH), page EG-3, and the Airplane Flight Manual (AFM), page 3-113. Both instances point out that once the landing gear handle is placed in the down position (after a failed retraction), the landing gear dump valve switch must be pressed and held for three seconds. The selection of the DUMP switch will not affect the dump system or illuminate the switch capsule, but will provide an alternate electrical ground path for energizing the normal landing gear extend solenoid. This will return the landing gear system to the normal landing gear extended configuration for landing. Once performed, this allows normal nose wheel steering and brake functionality for landing.
- The flight crew did select the gear handle to the down position after the failed retraction; however, they did not press the landing gear DUMP switch for three seconds. This left the landing gear out of sequence, which affected nose wheel steering and braking functionality. This is in reference to the condition the crew reported after landing regarding the dragging brakes.
- The aircraft was then taken to the hangar and placed on jacks. The landing gear system was reset to the normal condition. All landing gear normal and emergency operational checks were completed, as well as a check of the brake and nose wheel steering systems. No faults were found, and all systems operated normally.
- This incident stresses the importance of following established procedures (pre-flight and in-flight) and notes the delays that can be encountered when procedures are not followed.
If you land after leaving the pins in and fail to reset the landing gear dump valve switch, your landing gear selector valve is in the wrong position. The only way you can reliably get it into the correct position is to cycle the gear. And you have to do that on jacks.
But this takes us to my original premise: the G450 (and in this case the GV series) is not a conventional aircraft. In the four years since these Breakfast Minutes have been published, why hasn't anyone focused on the fact a gear swing is necessary? (I am guilty of this too.) It is because these airplanes are so complicated, nobody really understands them. I think if I found myself having attempted a gear retraction with the gear pins installed, I would (a) follow the checklist and press and hold that dump switch for 3 seconds, (b) land the airplane, and (c) do a gear swing on jacks even if Gulfstream told me it was unnecessary. I don't think they understand the system either and the only way to be sure is to cycle the gear. It is an expensive airplane, spending a day on jacks is better than the alternative.
Photo: G450 N667HS, Salzburg (LOWS), 11 Apr 2017 (Photographer: Roland Winkler)
In the GV series the flaps remain connected to the horizontal stabilizer through a series of computers and electrical motors. The result is system that is lighter and exhibits much better handing characteristics.
[G450 AOM , §2A-27-50 ¶1.A.] The horizontal stabilizer is an all metal structure mounted to the top of the vertical stabilizer at two points. The aft point consists of a shaft installed through an opening allowing the stabilizer to pivot. The front attachment is an actuator that moves the leading edge of the stabilizer up and down. The range of movement available for the horizontal stabilizer is from -1.00° (up limit) to -4.6° (down limit). The actuator is driven by the rotation of a torque tube within the vertical stabilizer that connects the actuator to an electric motor unit and gearbox located in the aft equipment bay.
The electric motor unit is operated by a single channel Flap / dual channel Stab Electronic Control Unit. The primary channel of the control unit is used in normal operation of the stabilizer when stabilizer position is coordinated with wing flap position. The normal control channel uses a set of motor windings powered by the Left main AC bus. The secondary channel of the control unit is used for operation of the stabilizer only independent of flap position in the emergency stabilizer mode. The secondary control channel uses a set of motor unit windings powered by the Right Standby AC bus, enabling emergency stabilizer operation during electrical malfunctions that require operation of the Hydraulic Motor Generator (HMG). Corresponding to the dual electric motor windings are two DC powered motor brakes that prevent movement of the motor drive shaft to inhibit uncommanded stabilizer movement. Both brakes are powered by the Essential DC bus. When a motor winding is employed by one of the control channels, the DC brake is first disengaged to allow the motor to turn in the desired direction. Additional protection against uncommanded stabilizer movement is provided by a locking ratchet installation, called a “no-back”, on the stabilizer actuator that prevents stabilizer motion from any source other than the stabilizer motor unit.
The system works great, except when something goes wrong. In the GV and G550 that isn't a problem because of their massive wings. For most conditions, a GV and G550 have lower approach speeds with no flaps than a G450 does with full flaps. The GV and G550 do not have emergency flap systems because they don't need them. In the GII, GIII, and GIV, the emergency flap system may have been invented by Rube Goldberg:
Figure: GIV Pitch flight control system, from GIV AOM, §2A-27-00, figure 3.
In those airplanes the flap selector valve sits just below and outboard of the copilot and the emergency system mechanically moved the valve. Simple. In the GV series that valve sits between the two main landing gear. Rather than provide a mechanical means of actuating the valve, the G450 has a switch to overcome electrical problems in the flap handle:
In other words, you really don't have a back up flap system. This impacts you in several ways, here are just a few:
- Despite what the manuals say, you cannot reliably lower the flaps without AC power during preflight. Yes it works on the GV and G550, but with the G450 you've got a problem. When we bought our airplane the procedure was identical to that in the G550 and it didn't work. Gulfstream denied this. I had one of their production pilots come out to show me what I was doing wrong and the flaps failed for him too. So Gulfstream changed the manual and that didn't work either. We repeated the "show me" routine twice more and then I gave up. So don't lower your flaps for the preflight until you have AC power, okay?
- The FSECU is a computer and sometimes computers get confused. If you move the flap handle and nothing happens, put it back to where it was and consult the checklist. If that doesn't work, land the airplane and reboot. Odds are the flaps will work.
- Earlier G450s had software flaws that failed to properly check the horizontal stabilizer brake. We flew like that for three years and didn't know it. (Neither did Gulfstream.) So ASC 086 fixed that. There is a test procedure given in the Before Starting Engines Checklist. I bring this up here only to illustrate that your flap system is so convoluted that the people who built the system didn't understand it even six years after the airplane was certified. If you have a flap problem, follow the checklist and don't get creative with your troubleshooting. Land the airplane. That's a pretty good rule for a lot of flight control issues: if the airplane is in a landable condition and you don't understand the problem, land the airplane. The crew of: Alaska Airlines 261 were heroic in their efforts, but hindsight allows us to see that they could have landed the airplane before trusting in the advice of people on the ground who were doing little more than guessing about a problem other people on the ground created.
Photo: N777TY after the crash, (courtesy Matt Birch vai.photography)
If the ground spoilers activate in flight, your aircraft takes on the flying characteristics of a brick. You need to be paranoid about deactivating them as soon as possible after takeoff and only arming them once you are assured the aircraft understands it is actually in the air. The pilots of Gulfstream V N777TY were not so careful. If you look at the wing with the ground spoilers fully deployed, you can see that the wing is no longer meant to be flying:
Photo: G450 with full flaps, ground spoilers and reversers deployed, from Eddie's aircraft)
So we have a few safeguards in place: both throttles have to be at idle, the flaps have to be greater than 22°, you need two sources of hydraulic pressure (one to deploy, the other to control), and the aircraft has to think it is on the ground. But these safeguards are not foolproof.
If you believed the combined WOW would save you, notice the system is hardwired to the switches on the main gear only. The combined WOW will give you a warning that something isn't right, but will not save you from an inadvertent deployment. Knowing this should impact the way you fly any GV series airplane:
- After takeoff, unarm the ground spoilers as soon as possible. If you bring the throttles to idle while the wheels are still spinning and if that flaps > 22° switch is faulty, you could have an inadvertent spoiler deployment. (Yes, those are two unlikely events.)
- When you do your external preflight, check the condition of your main gear WOW switches. They should be resting on the CAM and the CAM should be perfectly clean. (That CAM rotates as the gear extends and you could theoretically still have the "ground mode" commanded if there is any crud between the CAM and the switch.) Here is a video showing the cam rotating that should make this clear: G450 Main Gear WOW.
- Before you arm the spoilers, ALWAYS ensure you have four "A" indications that tell you all the electrons believe the ground spoiler system understands you are "A" for airborne.
Imagine you are flying into Chicago O'Hare in your G450. You have long become accustomed to having the charts displayed right on your avionics and seeing the green airplane follow you along on the airfield diagram and instrument approach plates. Wouldn't it be neat if you got that same functionality of those complicated SIDs and STARs? Well good news, Honeywell added that functionality in 2017. So, in early April, we loaded up the STAR and happily saw the altitudes in blue and the Geographic reference mark on the display.
Figure: Chicago O'Hare (KORD) Wynde 8 Arrival, from Jeppesen FlightDeck, page KORD 20-2N, 10 Feb 17
It isn't the hardest STAR in the world, but as G450 pilots we've become accustomed to this level of service, eh? But within a few minutes that display turned to this:
Photo: G450 "Retrieving Chart" error, from Eddie's aircraft.
To fully appreciate the magnitude of our concern, you need to see the video: G450 Retrieving Charts Error. The charts function of every display was inhibited and wouldn't come back. Would this mean we would have to navigate the taxiways of Chicago O'Hare without our moving map display? (Of course pilots without this capability are laughing right now. But we didn't have any paper charts.) Luckily we had an iPad with Jeppesen FlightDeck already loaded and ready to go. I must admit I am now more diligent about preflighting that iPad now.
We reported this to Gulfstream Technical Operations and were told, "We've never heard of this happening before, let us know if it happens again." Two weeks later it did. Gulfstream tried it on their simulator and couldn't duplicate the problem. They sent it to Honeywell and found that on aircraft without ASC 912 it would indeed happen. So now we know.
Photo: G450 Standby Flight Display, from Eddie's aircraft.
The Standby Flight Display has a mean time between failure that almost exceeds the life expectancy of the airplane, or so we are told. Our aircraft was only five years old when our SFD failed, and you can't fly without it under most conditions. I bring this up only to remind you that just because you could go without something in a previous airplane doesn't mean that you can in this airplane. Your IRS batteries, for example. Oh, you don't have any of those do you? Well here is an exercise you might appreciate.
- Pick up your MEL and figure out which eBatt you can dispatch without. (You can dispatch with one of the four bad.)
- What's that you say? The MEL doesn't mention eBatts at all? Here's a hint: what do the eBatts power?
- Now return to the MEL and look for IRU batteries.
- Gulfstream believes you can dispatch without the right avionics eBatt. When we had them write our MEL I changed "IRU batteries" to "Emergency Batteries" (eBatts) to which Gulfstream only laughed. They said it would be impossible to get FAA approval to dispatch without something called "emergency" anything. I said, "my point exactly." They were unmoved by my logic.
Photo: G450 eBatts, from Eddie's notes.
Photo: Gulfstream Customer Support Phone List.
Gulfstream G450 Aircraft Operating Manual, Revision 35, April 30, 2013.
Gulfstream G450 Operating Manual Supplement, G450-OMS-02, Extended Operations (ETOPS) Guide, Revision 2, April 2, 2009
Gulfstream G450 Quick Reference Handbook, GAC-AC-G450-OPS-0003, Revision 34, 18 April 2013
Gulfstream G450 Maintenance Manual, Revision 18, Dec 12, 2013
Gulfstream GIV Operating Manual, Revision 9, October 11, 2002