For want of one "line replaceable unit", a $73m drone was lost

We don't cover military drones here, but I'll make an exception for this fascinating accident report. We've all lost drones due to technical malfunctions, so we can sympathize with this. At least ours didn't cost $73 million.

From Defense Tech:

On August 11, 2011 Air Force ground controllers lost contact with one of the military’s most advanced — and expensive — drones, an EQ-4B Global Hawk as the jet flew high over Eastern Afghanistan.

Nine hours into an otherwise smooth communications relay mission using the Battlefield Airborne Communications Node (BACN), the plane was cruising at 51,000-feet above sea level 105 nautical miles northwest of Kandahar, Afghanistan — close to the border with Pakistan, in fact, the few news reports that emerged of the crash claim the jet actually went down inside Pakistan —   when a pilot from the 12th Reconnaissance Squadron out of Beale Air Force Base in California “lost all links with the payload,” according to a copy of the Air Force’s report on the incident that the service sent to DT. The pilot did everything he could to reestablish communications with the mammoth drone, but 25 seconds after losing communications, the plane began a high-speed fall to Earth. If plummeted so fast that “both wings and at least one of the lower aft fuselage fairings” were ripped off the jet as it fell. Three minutes later, the Global Hawk crashed into “remote, desert terrain approximately 4 nm from its last reported position and was destroyed,” reads the Air Force’s report. “the estimated loss is valued at 72.8 million.”

So, what caused this?

A single part — or Line Replaceable Unit, as the report calls it — came undone, interrupting the flow of electricity to the plane’s aileron and spoiler actuators — the tiny motors that control the movements of an aircraft’s flight control surfaces you know, the moving parts of the wings that control whether the plane climbs, dives, banks, rolls, etc. As expected, this disconnection rendered “the aircraft uncontrollable.”

(Critical parts that lose it like this one are called single points of failure, meaning that if these sometimes tiny and seemingly insignificant parts fail, the entire weapon system fails. Naturally, military equipment makers try o identify these and do all they can to ensure they won’t fail.)

Why did this single part become disconnected? “The board president also found, by a preponderance of the evidence, that the LRU [the critical part] installation methods were a contributing factor in the mishap,” reads the a summary of the report. Apparently, the screws holding the part in place weren’t tight enough and probably shook loose due to typical flight vibrations.

One other thing to note, the jet’s “avionics were not recovered from the crash site.” Let’s hope they were destroyed in the crash and the subsequent bombing of the wreckage by Air Force bombers and not scooped up by someone who could sell them to the Russians or Chinese.

Read the full reporthere:  

Views: 3148

Comment by Ellison Chan on March 8, 2012 at 8:31am

He Alan, you're girlfriend is right.  Putting you name an contact info on your drone is a good idea.  I mean if one landed in my backyard, with no contact information, I'd have to put an ad in newspaper to find out who it belonged to, but if the contact information was on it, it's just a matter of an e-mail.;

Maybe we should think about starting a Lost and Found UAV group, in this forum.

Comment by Rob_Lefebvre on March 8, 2012 at 9:33am

How timely.  I've been looking into better methods to connect all our equipment.  Here I am designing a redundant power system for my helicopter, and yet there's absolutely NOTHING stopping a servo wire from popping off. They aren't latched in ANY way.

I've been looking at latching Molex connectors, or 0.100" pitch terminal strips...

Comment by bGatti on March 8, 2012 at 10:54am


If you have a hexacopter with 3 power supplies, any one of them, or any one servo connector can pop off and you can still land slowly.

Comment by Rob_Lefebvre on March 8, 2012 at 11:03am

No, a *heli*copter.  ;)  If any servo connector comes off, it crashes.  

Comment by Matthew Schroyer on March 8, 2012 at 7:23pm

@Ellison - I don't know if anyone without proper security clearance can do a component-by-component comparison between the $73M Global Hawk and the $20M F-16. But following a little research, I found three reasons the unmanned EQ-4B costs more than an F-16.

1) Very advanced sensors. Remember, the Global Hawk is essentially a spy plane, so it is packed with expensive and advanced remote sensing equipment. One of these is the Enhanced Integrated Sensor Suite. To quote Raytheon's website: "The Raytheon-built EISS enables Global Hawk to scan large geographic areas and produce outstanding high-resolution reconnaissance imagery. To provide Global Hawk with its broad sensing, night vision and radar detection capabilities, EISS combines a cloud-penetrating synthetic aperture radar (SAR) antenna with a ground moving target indicator (GMTI), a high resolution electro-optical (EO) digital camera and an infrared (IR) sensor. A common signal processor, acting as an airborne super-computer, ensures that all elements work together."

2) Cost overrun. Aircraft like these aren't generally purchased individually, but in bulk via legal agreement with a contractor. That bulk purchase price includes the R&D costs. The per-plane figure you see is simply a division of the R&D costs plus the costs of the individual aircraft by the number of individual aircraft. A single Global Hawk likely costs less than $73 million to build, but you're seeing the R&D cost in that figure as well. The Global Hawk also overran its cost in development, at least in part because the Air Force cut its procurement numbers (economies of scale). Additionally, a jet like the F-16 has been produced in a high enough quantity over the years that the R&D costs were spread out over a lot of aircraft.

3) Age of equipment. The Global Hawk is SOTA, whereas the first F-16 was delivered in the late 70s. While the F-16 has been updated since, the equipment still not as current as the RQ-4 (the EQ-4B is a variant of the RQ-4 that includes a Battlefield Airborne Communications Node System).

Comment by Martin Szymanski on March 8, 2012 at 11:08pm

Reading the story I feel a critical root cause analysis needs to be performed. 

I personally use the lowest denominator method in problem solving. Minus (speculation) ;-)

Comment by Krzysztof Bosak on March 9, 2012 at 1:33am

@ian Forbes. 'take a joke man! Do you really think I am serious about the blue loctite (the loctite comment is what bothered you, seriously?)?'

Maybe I browse youtube too much and became annoyed of worthless 'Chuck Norris winning with Justing Bieber - priceless' template joke.

Comment by Brad Hughey on March 12, 2012 at 9:02am

Perhaps the lesson here is more one of design philosophy than procurement processes.  Aviation in general is very "old school" with regard to single-point-of-failure systems.  The old paradigm was one of accepting SPOF-fraught designs with obviously necessary perfectionist fabrication and conservative inspect/test/replace regimens.   Obviously this is an expensive way of doing things.  I readily concede that having two Casio watches instead of one Rolex in a system increases the chance of some sort of failure, but with the redundant approach, you'll always know what time it is (and you'll save a ton of dough).   

@Robert Lefebvre: Copters are (regardless of rotor count) vibration monsters, and electrical connectors have been the bane of my existence.  The best solution is to eliminate them wherever possible and just use solder.  In the model scale, the weight of the connector becomes an obvious issue, but it's a sure thing that these pin header connectors are terrible for maintaining electromechanical integrity.  All my connections between the RC receiver, APM, and ESCs are soldered.  Portability for bench repair is provided by one DB9 connector pair which is screwed together.

Comment by Helitrasher on March 13, 2012 at 1:17pm

Sounds like the U.S.A.F needs new Guns (70mil worth) !

Comment by Dr John Lannigan on March 14, 2012 at 5:56am

After reading the report, i cannot understand why 

"Specifically,apartial separation of the LRU-X-JXconnector led to interruption oelectrical power to aileron and  spoiler flight control actuators, rendering the aircrafuncontrollable."</</body>


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