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Strobe Fault Indicator


Figure: Strobe Fault Indicator Quiz, from Eddie's notes.

Ask any Gulfstream pilot for the correct answer to the puzzle shown above — which is the good strobe light fault indicator and which is the bad — I am betting he or she will probably get it wrong. I did. But it isn't our fault, there is nothing in the books that tell us what to look for. I'm not even sure I've got the right answer because I am just going on anecdotal evidence of one airplane. If you know better, please click the "Contact Eddie" button below and let me know.

Oh, the answers:

  1. B
  2. C
  3. A

Other things I didn't know about the strobe light system:

  • The system defaults to the top strobe light for both wing tips and the tail.
  • It only goes to the bottom strobe if there is a problem with the top.
  • A tripped fault indicator could mean a bad top bulb, a momentary electrical spike, or a hard landing. In any case, you need to reset the fault indicator. If it trips again, you need to change the bulb.

What we do know

The books make us check these things but there are no pictures and no descriptions about what is good and what is bad.

G450 Aircraft Operating Manual

[G450 Aircraft Operating Manual, §02A-33, ¶2.B.] Exterior white strobe lights increase the visibility of the aircraft to other traffic while airborne. The strobe lights are installed in each wing tip and in the tail cone at the rear of the aircraft fuselage. Each installation consists of two flash tubes, each with a triggering transformer and a single power supply with a fault indicator. The STROBE switch in the EXTERIOR LTS section of the overhead panel activates the lights. When the switch is depressed to the ON position, the blue ON legend within the switch illuminates. When the lights are operating, each light is synchronized with the other lights, and all three lights flash simultaneously at 42 to 52 times per minute. Only one of the installed flash tubes is powered, with the second acting as a spare. If a flashtube failure is detected by the power supply, the second flashtube is automatically activated and a fault indicator at the lights provides a visual indication that the first flashtube has failed. The fault indicator can be manually reset.

[G450 Aircraft Operating Manual, §03-01-20, Step 46.] [Right] Wing Tip . . . Check strobe light fault indicator for failure.

[G450 Aircraft Operating Manual, §03-01-20, Step 124.] [Left] Wing Tip . . . Check strobe light fault indicator for failure.

The manual doesn't ask you to check the tail strobe, but you should.

G450 Maintenance Manual

[G450 Maintenance Manual, § 33-42-00, ¶3.A.] There are three anticollision strobe lights. One anticollision strobe light is installed in each of the wing tips and the third anticollision strobe light is installed in the tail cone stinger. Each strobe assembly consists of a light assembly with two flashing tubes, a dedicated power supply and a locally mounted fault indicator. Each strobe is synchronized to the other strobe lights and flashes at 47 ±5 flashes per minute. Each strobe illuminates only one of the flashing tubes at a time. Once the first flashing tube fails, the second flashing tube automatically turns on and a fault signal is sent from the power supply to indicate the first flashing tube has burned out. This fault signal latches a locally mounted manual reset fault indicator.

There are no pictures of the fault indicator or descriptions of what is good or bad.

What I Think is True

After four years one of our lights finally went bad, and here is what we saw.

Fault Indicator Negative (Two Good Strobes)


Photo: From Eddie's aircraft.

Both strobes work on this wing tip and the fault indicator is half-black, half-gray.

Fault Indicator Positive (One Good, One Bad Strobe)


Photo: From Eddie's aircraft.

One of the strobes does not work on this tail cone and the fault indicator is half-black, half-white.

Fault Indicator Negative (Two Good Strobes)


Photo: From Eddie's aircraft.

We reset the fault indicator and now it is half-black, half-gray again.


Gulfstream G450 Aircraft Operating Manual, Revision 35, April 30, 2013.

Gulfstream G450 Maintenance Manual, Revision 18, Dec 12, 2013

Revision: 20140326