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Adiós, Space Fence

While most news outlets were freaking out about killer pythons, the Japanese helo carrier, or the 68th anniversary of the bombing of Hiroshima, the US Air Force was quietly preparing to shut down Space Fence, one of the oldest but most productive parts of its space surveillance network.

It’s also one of the few facilities that can provide 24/7 “uncued detection” capability… which is nerd-speak for the ability to find things in orbit that nobody expected to be there (ie. space junk).  Contrary to what Hollywood likes to show you, it’s impossible to track every single object of space debris.  There are over half a million distinct objects, some smaller than a penny, and no one nation (or even group of nations) has enough radar or visual coverage to follow them all.  In fact, the US Space Surveillance Network has only 6 facilities worldwide dedicated to on-orbit detection and tracking; Space Fence was the largest and most effective of them, spanning the continent at the 33rd parallel.


Space Fence is the red line stretching across North America

Why is the closure of this capability important, you ask?  It might be easier to have some visual reinforcement.


STS-7 window impact

This is what a mere fleck of paint did to a cockpit window on OV-099 Challenger during the STS-7 mission, back in June of 1983.  The pit you see there is only 1mm in diameter, but remember that paint is probably the most innocuous bit of debris one can run into when travelling 17,580 miles an hour.   During STS-59, OV-105 Endeavour experienced similar window damage, and the object actually penetrated half of the window’s total depth.  That’s kind of a big deal.  Other STS missions have seen micro-collisions where objects have punched right through the orbiter’s silvery radiator panels.  Objects like this paint fleck are too small for Space Fence to detect and track, but there are literally hundreds of thousands of larger objects.

Despite being several decades old, Space Fence is still relevant today because it has a longer reach than most other sensors, and because it can do its work un-cued.  In other words, it detects without being specifically tasked to look for a known or unknown object in a given region of orbital space.  It is responsible for around 40% of the observations on the 23,000 objects the Department of Defense currently tracks.

Though part of a broader surveillance network, the VHF Space Fence is crucial because it can track objects up to 24,000 kilometers away. Other sensors in the network generally track objects at altitudes lower than a few thousand kilometers, [Brian Weeden, technical adviser at the Secure World Foundation, a nonprofit organization dedicated to space sustainability] said.

“The Space Fence is very important as it gives an ‘uncued tracking’ capability,” Weeden said. “Because it’s constantly transmitting, it can detect objects without being tasked to do so. There are some other sensors in the network that can do uncued tracking to some degree, but the Space Fence is rather unique in the sheer size of the detection coverage it has.”

Gruss, Mike.  Shelton Orders Shutdown of Space Fence.  SpaceNews, 6 August 2013.

Granted, the current Space Fence is a little long in the tooth and suffers the additional handicap of being based on 1960s technology.  Thanks to sequestration, not only is the current capability being forced to close, but its future replacement is also stuck in limbo—waiting for the Pentagon to decide what projects it can reasonably afford.  Meanwhile, there are about 500,000 debris objects too small (from 1-10cm in diameter) for the current space surveillance network to keep tabs on.  And their numbers will only increase.


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Even hundreds of miles away, a storm can give you a bad day

With Air France 447’s experience in heavy weather front of mind, it’s important to recall that aircraft at cruise altitudes are not normally put in peril by a storm front along their route of travel.  They tend to be most dangerous to aircraft that are in the takeoff or landing phase, when the aircraft are travelling the slowest and aircrews have the greatest amount of workload.  An Air Force C-130 narrowly avoided a Colgan 3407-like stall on approach through quick recognition and fast action by the aircrew.

“We were on our initial approach into Al Asad,” said Capt. Andrew Gillis, a 737th EAS C-130 aircraft commander and native of San Jose, Calif. “We were the third aircraft to go in. No one else reported any issues. In the middle of our approach, it started getting real rocky, and our air speed indicator ended up bouncing up and down plus or minus 20 knots.”

Falling back on countless hours of training and simulations, Captain Gillis advanced the throttles to max power to break off the descent and go around again. There was only one problem.

We had absolutely max power from the airplane,” Captain Gillis said. “There’s a specific escape maneuver, and we were in the process of doing that maneuver, but the airplane was still sinking.

— Staff Sgt. Thomas J. Doscher.  “Quick recognition, action saves C-130 aircrew, soldiers“, 386th Air Expeditionary Wing Public Affairs, June 3rd, 2009.

Ouch.  Throttles firewalled at 1,800 feet AGL, and still going down; not a good situation to be in.  What is really remarkable is that between problem detection and problem resolution, the aircraft lost just 800 feet of altitude despite being in a remarkably perilous situation for over seven miles. And 1800 feet is not a lot of room to play with when we’re talking about a stall or high sink rate situation.  It is a good thing the crew diagnosed the situation so rapidly and took corrective action.

Even more interesting, the high winds they encountered were actually caused by a large storm front several hundred miles away.

With the winds making a safe landing impossible, the crew headed for home, enduring another 30 minutes of intense turbulence. 1st Lt. Jeff Stanek, the aircraft’s navigator, said the wind shear and turbulence were caused by a massive storm front hundreds of miles away.

“There was a huge storm front the size of California that moved over Turkey,” said the native of Marlboro, Md. “And it moved faster than anticipated. We were clear of the actual storm, but the gust front in front of the storm is what we hit.”

Bravo zulu to the whole aircrew; you guys saved 45 passengers (as well as yourselves).

Colgan Air 3407

There has been some good blog coverage of the Colgan 3407 accident lately.  For a perspective on the Catch-22 finances and schedules that the regional airlines (and their pilots) find themselves in, read Aviation Mentor‘s terrific post.  For an in-depth examination of the FDR (flight data recorder) and CVR (cockpit voice recorder) data, see Blogging at FL250.  Probably the best overall description of the events leading up to the fatal crash, far better than anything you will find in bowdlerised media accounts, whether print, web or television.

It’s hard to know what to make of this incident, as the accounts you get in the media inevitably focus on the sensational (CVR, shrieking final moments, etc) as opposed to the instructive (FDR).  What has become apparent out of the data is that the aircraft didn’t suffer a tailplane stall so much as an ordinary (wing) stall, something pilots all over the world are taught to recover from by pushing the nose down and increasing the throttle.  Yet the captain of Colgan 3407 did the opposite, and it’s not entirely clear why.  Media accounts paint him as inexperienced at best, and at worst they hint at several failed checkrides and come nigh to declaring him incompetent.

My own sense is that one doesn’t get past a PPL, instrument rating, night rating, commercial rating, multi-engine rating, ATP, type rating, several FO checkrides and captain checkrides by being an incompetent boob.  It strains credulity.  Which is not to say that pilots can’t occasionally be stupid, but they are not habitually stupid.  So how to explain pulling up on the yoke when standard stall recovery is to push the yoke forward?  A panic reaction?  Or did the captain mistakenly believe they were experiencing a tailplane stall (whose recovery procedure is to pull up), only to belatedly realise that it was a wing stall—but by that time, all manoeuvring altitude had run out.

The “how” is readily apparent from the FDR, but it’s hard to answer the “why” without having the aircrew able to answer for themselves.

UPDATE:  Sam at Blogging at FL250 cranks out another home run with his latest post.  In it, he unlocks the mystery of why the captain might have acted contrary to standard to stall recovery procedures.  The short version is that the Practical Test Standards for the ATP rating do not require realistic simulation of an approach or takeoff stall, where the aircrew is distracted.  This allows airlines to condition their pilots to “ride the shaker”, maintaining attitude and altitude during the stall, waiting for power to wrestle the airplane back up to a safe airspeed.  The practical outcome is that the aircraft remains in a stall longer than necessary, and when you’ve got relatively little altitude to play with—on takeoff or approach—that may have dire consequences.

Like one of his commenters says, if he’s not in the training department at his local airline, he ought to be.

Intuition, a little too late

In media accounts of the Colgan 3407 cockpit voice recording, there is this little snippet that is both tragic and ironic:

Seven minutes later, [Captain Marvin] Renslow complained of the ice that was forming on the plane’s windshield and wings.

“That’s the most I’ve seen … most ice I’ve seen on the leading edges in a long time,” Renslow said.

A moment later, the co-pilot, Rebecca Lynn Shaw, complained of her own inexperience.

“I’ve never seen icing conditions,” she said. “I’ve never de-iced. I’ve never seen any. I’ve never experienced any of that. I don’t want to have to experience that and make those kinds of calls. You know I’d ‘ve freaked out. I’d have like seen this much ice and thought oh my gosh we were going to crash.”

Moments later, the crew lowered the plane’s flaps and landing gear, and the plane quickly encountered trouble.

— Jerry Zremski.  ” Pilot: ‘Most icing I’ve seen’; Co-pilot: ‘I’ve never de-iced.’ “, Buffalo News, May 12th, 2009.

Maybe sometimes it’s best to go with your gut reaction.

A Cautionary Tale

While reading some of the updated news about Colgan Air 3407, I was reminded of a harrowing incident recounted on an aviation blog.  I include it here not as prognostication on what happened to Colgan 3407, but as a reminder that when flying into inclement weather, it is critical that the aircrew work together professionally and keep flight safety front of mind at all times.

runny_vortilons[The captain] has spoken to the boss, and they have decided that we will continue on and get back to our base. That means at least 1.5 hours in the ice, instead of the 30 min we have just completed. I am not happy about this, and we get into a screaming match in front of everyone. Classy. Eventually I give in and get into the plane. Though I am NOT happy about it. It is my leg to fly, but I refuse, stating that since my input was not required while making the decision to do this leg, I will not fly. I am a passenger. What else can I do, besides stay there, alone, cold, with no where to go.

We take off.

We start picking up ice.

Lots of ice.

We change altitude.

Still more ice.

We are now unable to maintain altitude.


The captain comments that it ‘doesnt’ look as bad as the last leg’. I point out that we have an ever lower airspeed that before, and are using a higher power setting on the engines. In fact, we are at max power.

We are now drifting down towards the ground, the windshield caked in ice so bad we can barely see out. The ice on the wings extends back a foot and a half back from the boots. I feel ill imagining what the tail is looking like. We are inching closer and closer to a tail stall, I can just feel it.

— Anonymous pilot, “The Night of Ice“, Sulako’s Blog, April 8th, 2008.

Read the whole thing.  That particular aircrew is lucky to be alive.

Image “Runny Vortilons” from Fiveholer’s Flickr stream.

RELATED: Neptunus Lex presciently points to a 1998 NASA video describing the tailplane icing phenomenon.