Updated list of D-Chall dives

James Cameron, Sylvia Earle, and John McCosker can be heard in the first half of today's Science Friday on NPR. 

Google-users can now dredge up a few more bits and pieces about D-Chall's construction details, as posted by companies or experts who participated. I'm almost ready to put out another Sub-Spotters Photogram.

And the Deepsea Challenge website published a few additional expedition notes covering the end of Phase I. That helps round out the third draft of my list, but I still don't get to the official total of 13 actual D-Chall dives unless there were multiple test dives in Jervis Bay.

Date	Location	Max depth (feet)	Notes
1/26/12	Dock at Garden Island Naval Depot, Sydney Harbor	< 5	Checks for buoyancy and water tightness
1/31/12	Dock at Garden Island Naval Depot, Sydney Harbor	< 5	First time JC piloted sub
2/01/12	Jervis Bay, S of Sydney	Reached ocean    floor	Reduced use of heat-emitting equipment, to reduce high temp in pilot sphere
?	Jervis Bay, S of Sydney	?	One or two additional test dives by JC
2/21/12	Jacquinot Bay, Papua, New Guinea	0	Sub launched with JC, but aborted after 1 hr.    Stayed on surface
2/22/12	Jacquinot Bay, PNG	0	Scrubbed due to camera-control problems
2/23/12	Jacquinot Bay, PNG	3,250	Successful dive, photography, moved horiz at 3 kt, and rendezvous with lander Mike and ROV Quasar operated from above
2/27/12	Jacquinot Bay, PNG	0	Scrubbed
2/28/12	Jacquinot Bay, PNG	12,000	Successful rendezvous with landers Mike and Andrew, maneuvered 5 km horiz with guidance from ship
3/04/12	New Britain Trench	23,818	On way to NB Trench bottom, tried to stop 5 kt descent with large dumps of trim shot, then ascended slowly; then dropped ascent weights
3/07/12	New Britain Trench	26,791	Successful dive to trench bottom for photography – maneuvered 1.5 km horiz, 300m vert
3/21/12	Challenger Deep, Vicinity of 11° 22' 59 N, 142° 35' 20" E	“Nearly seven miles”	“Unpiloted” test dive; pressure “almost 8 tons per square inch”
3/25/12	Challenger Deep, Vicinity of 11° 22' 59 N, 142° 35' 20" E	35,756	First solo dive to bottom of hadal zone; photography; part of one push-core sample brought up; surfaced at local noon
4/01/12	West of Ulithi Atoll, in Zowariyau Passage	3,700	RA's first dive; rendez with Mike and ROV Quasar; 25 min descent; 6 hr at bottom; near-vertical scarp; Photography successful
4/04/12	Ulithi Atoll	800
4/04/12	Ulithi Atoll	500	JC piloting

Every Wreck Has Four Corners

As History Channel-watchers may have gathered from the ads, tonight is Titanic night. I participated in one of those, Titanic at 100: Mystery Solved. It gave me a chance to meet long-time Titanic experts Parks Stephenson, Ken Marschall, and Bill Sauder. Here's a promotional photo from History that the NYTimes used in its wrapup of the weekend's Titania-mania programs.

I'm the tiny dot above the boiler, standing with Ken in a "virtual hangar." Lone Wolf's crew filmed the segment in November with a Red One camera on a crane in a real hangar at a former naval air station in Brunswick, Maine. Edgeworx Studios did the special effects.

I always prepare my own set of briefing notes before heading off to help in a documentary, and the purpose of this post is to give a little background about one of the terms highlighted in my notebook, the "four corners" of a site. If a principal investigator says that her team has found the four corners, it can mean that the team knows the location of all four extremities of a plane: nose, wingtips, and tail. Or she can mean that the team has identified all material of interest, wherever it landed.

It's possible for important pieces to land quite far from the main body of the aircraft, so in such cases it wouldn't be enough to confine work within the polygon marked by the two wingtips, nose, and tail empennage. 

One such case is the broken fan disk from the No. 2 engine on Flight 232. Because that engine's catastrophic failure had cut hydraulic lines that led eventually to the crash landing at Sioux City, finding pieces from the fan disk was critical to identifying the root cause. 

Three months passed. Then a farmer found the fan-disk pieces in his cornfield near Alta, Iowa, 55 miles east of the crash site. The fan disk had fallen from the plane in flight. It was so important the NTSB worked up a debris map specifically for this assembly:

When an airliner crashes, a process begins that can take well more than a year to complete. Here's a profile from Popular Mechanics explaining how the NTSB tackles a light-plane crash. 

Top priority is locating and rescuing any survivors, followed by recovery of human remains and crash-site preservation, then marshalling of evidence. 

That includes interviews with anyone having first-hand knowledge, locating and mapping physical evidence, preserving those pieces, and locking down relevant information whether paper or electronic. The latter includes:

• Downloads from recovered aircraft digital flight data recorders and cockpit voice recorders
• Weather reports
• Air traffic control records
• Maintenance and personnel logs
• Medical records
• Emails between crew and operator
• Voice communications with the aircraft

Lately that evidence trail is likely to include ACARS transmissions (short for Aircraft Communications Addressing and Reporting System). 

In the case of the Air France Flight 447 that crashed on June 1, 2009, the Airbus 330-200 had an ACARS unit that transmitted routine navigational fixes at regular intervals. It also sent a burst of telemetry in the final moments, reporting two dozen alarms going off on the flight deck.

Locating the crash site is a critical early task, and with very few exceptions this succeeds. In cases where no local information or signal from the aircraft pinpoints the impact, the first job is to identify the LKP, and anchor a search around that point on the map. LKP stands for “last known position.” Think of the LKP as the center of a bullseye. Searchers draw concentric rings around it, marked in nautical miles.

In the case of Flight 447, the last ACARS transmission was the best information anybody had on the LKP. Here's a diagram from BBC published in June 2009. The box labeled 0214 Greenwich Mean Time marks the LKP.

While the Airbus had emergency-locator radio beacons on board such devices don't help when a plane crashes far from shore. The heavy wreckage sinks, taking beacons with it. Locator radio frequencies don't transmit more than a few hundred feet through water, and the ocean here was 12,000 to 13,000 feet deep.

Given the LKP to go on, search airplanes located 51 bodies and large floating pieces of the Airbus within four days. Here's the tailplane:

But the bulk of the wreckage, along with the digital flight data recorder and the cockpit voice recorder, had come to rest somewhere near the Mid-Atlantic Ridge. While most of world's spreading-zone ridges are deep underwater, part can be seen in Iceland:

This led to concern that if the wreck came down in such rugged territory, it might never be found. 

The first phase of the search assumed it would be possible to locate the wreckage in the first few weeks by the Underwater Locator Beacons, aka "pingers." It failed. That was a puzzlement, because searchers should have had the benefit of acoustic pings for homing. 

Pingers are bolted directly to the data storage units for the cockpit-voice and flight instrument recorders. And they're rated for 20,000 feet of depth and at least 30 days of acoustic transmissions. 

The pingers are small cylindrical objects with self-contained batteries. They activate automatically on contact with water. Here's the typical setup:

(Coincidentally, pingers were in the news a few months ago, because salvors at the Rena wreck site attached them to dozens of cargo containers likely to break off the deck before the crane could get at them.)

Searchers used deep-diving hydrophones, towed behind ships moving along a search grid, to listen for signals that should have been weak but detectable. Given that searchers knew the LKP, and also had a good idea of how much farther Flight 447 could have flown from that point, there was optimism about picking up the pings if they moved quickly enough. 

Except that no pings were heard, ever. Could ocean currents have carried the wreck a considerable distance? Though data on deep currents at the time of the crash was in short supply, perhaps computer models could fill the gaps. The French investigative agency, the BEA, convened a Drift Committee to estimate the net effect as wreckage passed through different layers. 

Meanwhile another theory posited that the pilots might have turned around and headed the plane to Brazil, and therefore the LKP was a blind alley.

Two more phases of the search followed, using increasingly sophisticated side-scanning sonar. Still no luck; there was some doubt now that the wreckage would ever be found. So in July 2010 BEA had the scientific analysis firm Metron of Reston, VA, take a fresh look at all the sweeps to date, and all the signal returns. 

Metron used a tool that I strongly recommend techno-watchers become more familiar with: Bayesian inference. Having heard about its use in a wide variety of settings, I believe Bayesian inference (in the right hands) can help society manage risks from complex, high-energy systems. Not eliminate the risks, but manage them. It does this by modifying old thinking with new information. Rather than forming a single idea and sticking to it (a pattern I see a lot), Bayesians continually refine their knowledge of the world. As long as everything ties back to the real world, and all homework is shown, Bayesian inference can be a very powerful tool.

Back to our story. In January 2011, Metron reported back to the BEA: while searchers had reasonably concluded that the wreck must be far away from the LKP (because the pingers hadn't been heard near the LKP, and surely pingers wouldn't fail), the Bayesian approach suggested the pingers might have failed even so, and side-scanning should pay more attention to the immediate vicinity of the LKP. 

Metron singled out several targets of what appeared to be man-made objects. These had not been fully investigated during early searches.

Armed with this insight, the search fleet went back to the site for a fourth attempt to find Flight 447. Side-scanning autonomous subs found the wreck within a week, and very close to the LKP.

As tagged with photos and published in the 2011 BEA report, the wreckage was laid out like this:

Note that the field was fairly compact. This confirmed that the plane did not break up in midair. Rather it hit the water at high speed.

Besides assisting in the hunt for the long-lost wreckage of 447, two autonomous sonar-subs owned by the Waitt Institute (dubbed Mary Ann and Ginger) were key players in the 2010 survey that re-imaged Titanic and eventually led to the History Channel show "Mystery Solved" show tonight. 

Here's a Waitt Institute video showing the Remus 6000 subs in action. Here's an info-sheet from Kongsberg Maritime, which builds them in conjunction with Woods Hole. And here's the deep-diving Mary Ann herself:

Investigators' Case File: When crash sites can't be found

As a nod to Titanic week, I'll post a note about beacons and debris fields in a bit. But fragments can't be flagged, tagged, or mapped on a grid unless the site is found first. What if the airplane never turns up?

Lost airliners may seem a problem confined to the wayback era of Lost Horizon ...

... a novel in which a DC-3 crash-landed in the Himalayan fastness, leaving the survivors on their own. Fortunately for them, the friendly burg of Shangri-La was just around the corner.

Do airliners still stray off the map in the post-WW2 era? That is, go missing, and stay missing?

Yes, but not often! One was Northwest Airlines Flight 2501, a westbound Douglas DC-4 that broke up in a storm over Lake Michigan on the night of June 23, 1950. Rescuers pulled human remains and floating debris from the lake's surface, but the plane's metal wreckage never turned up, despite sonar-assisted efforts in the last ten years. Most likely cause: in-flight breakup due to severe storms in the area.

Another was an Air Charter DH-90 Dragonfly, registration ZK-AFB, which went missing on a February 12, 1962, sightseeing flight from Christchurch to Milford Sound, NZ. The airframe looked like this:

Despite what's said to be the biggest search and rescue effort in New Zealand's history, the plane was never found.

The most recent missing-airliner case that comes to mind was a Pakistan International Airlines Fokker-27 turboprop with the call letters AP-BBF. It carried 54 people. Here's what a Fokker-27 looks like:

The last information about the August, 25, 1989, flight from Gilgit to Islamabad was a routine report transmitted seven minutes after leaving the airport. 

Despite an intensive search along the flight path, no trace of passengers or plane has been reported since then. A focus for the search was Nanga Parbat, this 26,660-foot peak:

Two climbers who were on the peak at the time said they may have seen the PIA plane go by.

Next, a post explaining why it took so long for searchers to locate the submerged digital flight data recorder and cockpit voice recorder from Air France 447.

D-Chall's Mast and Upper Section: Another photogram

Here's a second photogram, now focusing on the sub's upper parts.
 
Here's a link to a short video about the beacons in the mast. 
Beacons and backups are important for the pilot's peace of mind for at least two reasons: a delayed ascent, combined with a fast-developing tropical storm, could make D-Chall hard for Mermaid to find. That would be bad, because the pilot can't get out until Mermaid's crane has lifted it from the water.

Note that the green shell is not syntactic foam, despite many online diagrams to the contrary! I feel safe in guessing it's a fiber-reinforced plastic, or FRP. The hulls of racing yachts use carbon-reinforced fiberglass, sometimes laid up as a sandwich of two outer FRP layers with a foam filling. 

From what I can tell, the syntactic foam known as IsoFloat is visible on D-Chall's exterior at only a few locations, where it appears as blocks of white plastic. This looks like one of those locations:

Another angle showing the high-tech foam around the hatch can be seen in this screen grab from a video on the website:

Deadly Avalanche at Base Ghyari: Fallout from a most peculiar conflict

Regarding the rescue operation that began after an avalanche buried more than a Pakistani troops at the Ghyari base near the Siachen Glacier in Kashmir ... information on the area's history and geography is available at SiachenGlacier.com.

Here's a map of major Pakistani and Indian bases, from Mangalorean. I marked the avalanche site with a red circle.

This photo is said to be a shot of the base at Ghyari: 

Here's a photo of the vicinity, which is part of the Karakoram Range, from The Telegraph:

Note the helicopter at the center of the photo. 

For those curious about the strange high-altitude war along the Siachen Glacier that lasted from 1984 to 2003, the following is adapted from my book on the social history of helicopters for Random House, The God Machine. Here's a satellite photo, from SiachenGlacier.com:

The conflict was highest-altitude war in history. While there's been no major fighting there for almost a decade, troops on each sides still hold positions under very difficult conditions, living on ridges in plastic igloos like these:

The dispute originated with a 1949 disagreement over the exact course of the India-Pakistan border where it passed through the old kingdom of Kashmir. The disagreement was academic until an Indian Army officer noticed in 1977 that the Pakistanis were issuing permits for mountaineering parties to climb certain high mountains that India claimed. Now the race was on to control the Siachen Glacier and three high passes.

In a secret mission called Operation Meghdoot (Sanskrit for "Cloud Messenger"), the Indian Army used helicopters to reach the high ground first, in April 1984. Indian troops planted fiberglass igloos at altitudes as high as 22,000 feet in the Saltoro Range forming the west rim of the glacier. 

Most of the fighting was conducted with cannons and mortars, which fired whenever the weather was clear enough to pick out a target. One workhorse was the Indian Air Force's Mi-8:

... which brought supplies and even light cannons to 17,000 feet. Troops dragged the hardware the rest of the way, a few agonizing feet at a time.

While the lower-altitude Pakistanis could depend on trucks and pack animals, Indian forces were totally dependent on helicopters for the last stage of their supply chain, and for lifting out hundreds of men debilitated by the conditions. The machine of choice was the Aerospatiale Lama, along with an Indian-manufactured version called the Cheetah. This photo from BharatRakshak:

For almost 20 years, each side attempted to leapfrog the other, looking for gun emplacements that could shell but not be shelled in return. One solution: the high-altitude helicopter raid. 

In April 1989 a Lama helicopter carried a squad of Pakistani troops one at a time and dropped them onto a saddle-shaped ridge at Chumik Pass, altitude 22,100 feet, allowing them to sneak up on an Indian post.

Labeled Photogram, for the Sub-Spotter Crowd

I haven't seen diagrams offering much detail about Deepsea Challenger, which presumably will be going back to the Acheron Project shop in Leichhardt, Australia, for maintenance, now that Phase I is over.

Bloggers abhor a vacuum, so here's my addition to the mix: not a diagram, but a photogram. If there's interest, I'll put up one featuring D-Chall's lower pod and payload bay, and another on the upper end (carrying beacons, antennas, and acoustic transponders).

Label info is gleaned from photos and journal entries on the project website, plus other published interviews like this one.

D-Chall's Excellent Adventure: End of Phase I

Mermaid Sapphire is back at Apra Harbor, Guam, marking the end of the Phase I voyages of D-Chall, as backed by the National Geographic Society and Rolex. (D-Chall is my abbreviation for Deepsea Challenger; I'm tired of typing the full name and if J Lo can thrive under an abbreviation, the sub can too.) 

Here's a newly released photo, taken a month ago by one of the unmanned craft:

This photo is of interest because it's one of the few photos of the lower pod that shows the science door as swung open by its hydraulic actuator. Here's a closeup, including what look to me like sample containers:

For the participants, Phase I must have been an exciting combination of sea trials, actual science, and lessons learned. The expedition journals don't reveal any close shaves, but do suggest that the missions below 20K feet were pretty hard on some equipment, particularly the battery buses and hydraulic manifolds. 
There was a glitch in ballasting on the March 4 dive that must have given James Cameron an unwanted thrill, though it never involved the critical hardware, the ascent-weight release system. 

The good news is that there was plenty of redundancy and the team managed the inevitable problems as they arose. And it was complex! Take a look at this closeup from an NGS photo of the lower pod manifold area.

Geeky readers will note that some of the lines are labeled:

Back to the big picture. 

While Phase I was a qualified success, the press release is guarded about the scale of plans for Phase II, given the operational costs (like a million dollars a month, just for the vessels; team personnel, mission support, and expendables would be extra). The role of unmanned deep-divers Mike and Andrew will be an interesting question. As I surmised in this March 28 post, the science team on Barakuda kept the twins busy following the deep-dive media blitz. That included a trip to the Sirena Deep.

The incremental approach when deploying D-Chall (progressively nudging the envelope, followed by close analysis of each mission, repairs, and retraining) is the kind of thing test pilots do. It pays handsome returns in safety dividends. 

In Inviting Disaster I wrote about how seemingly dangerous work can be rendered survivable by a thoughtful, incremental approach. One WWII-era example was Royal Aircraft Establishment pilots who tested the efficacy of barrage-balloon cables by ramming them with their airplanes.

The Deepsea Challenge expedition modified its plans at several points. Apparently the original schedule did not include deep trials between Australia and the Challenger Deep, but Papua, New Guinea, was on the way, so the team decided to stop there for trials to 27K feet, at the cost of some sea time over the Deep. Probably a good thing ... 

Here's my second draft of D-Chall's dives and dates. The website says 13 trials or dives have been made to date, so I may be missing one or have it in the wrong place. Note: the last item in the table was a lander dive, not a D-Chall plunge. I'd imagine that Phase I involved many lander dives that are not on this list.

Date (Local)	Label	Location	Max depth (feet)	Notes
01/26/12	First submersion – no pilot	Dock at Garden Island Naval Depot, Sydney Harbor	< 5	Checks for buoyancy and water tightness
01/31/12	First piloted submersion	Dock at Garden Island Naval Depot, Sydney Harbor	< 5	First time JC piloted sub
02/01/12	Piloted open-ocean test	Jervis Bay, S of Sydney	To ocean floor	Reduced use of heat-emitting equipment, to lower sphere temp
02/21/12	First attempt, test dive to 3K feet	Jacquinot Bay, 3 mi offshore of Papua, New Guinea	0	Sub launched with JC, but aborted after 1 hr. Stayed on surface
02/22/12	Second attempt, test dive to 3K feet	Jacquinot Bay	0	Scrubbed due to camera-control problems
02/23/12	Test dive to 3K feet	Jacquinot Bay	3,250	Successful dive, photography, moved horiz at 3 kt, and rendezvous with lander Mike and yellow ROV operated from above
02/27/12	Attempted test dive to 12K	Jacquinot Bay	0	Scrubbed
02/28/12	Test dive to 12K	Jacquinot Bay	12,000	Successful rendezvous with landers Mike and Andrew, maneuvered 5 km horiz with guidance from ship
03/04/12	First Dive, New Britain Trench	New Britain Trench	23,818	On way to NB Trench bottom, tried to stop 5 kt descent with large dumps of trim shot, then ascended slowly; then dropped ascent wts
03/07/12	Second Dive, New Britain Trench	New Britain Trench	26,791	Successful dive to trench bottom for photography – maneuvered 1.5 km horiz, 300m vert
03/21/12	“Unpiloted” test dive to Challenger Deep	Not specified	“nearly seven miles”	Pressure “almost 8 tons per square inch”
03/25/12	First solo trip to deepest point	Challenger Deep (vicinity of 11.3632, 142.5770)	35,756	Successful dive – first solo dive to bottom of hadal zone photography; part of one core sample brought up; surfaced at local noon
04/01/12	First Dive, Ulithi Atoll	West of Ulithi Atoll, in Zowariyau Passage	> 3,000 ft	RA's first dive; goal to rendez with Mike and ROV quasar – result ?; Photography successful
04/02/12	Possibly a second piloted dive off Ulithi	Ulithi Atoll ?	- ? -
04/03/12	Dive by lander from Barakuda	Sirena Deep, Mariana Trench Marine Natl Mon	>35,000 ft	Sampling and photography

Deepsea Challenger: Back in action?

#DeepseaChallenge relayed this tweet seven hours ago:

James Cameron ‏ @JimCameron  Sub co-designer Ron Allum made his first @DeepChallenge dive today. 3,600 ft & he dove the sub like a champ. Awesome pix! #deepseachallenge

That would make sense, because Allum knows as much about the sub as anyone. But there are no follow-ups yet on the project's Facebook page or website. Soon, presumably.

The ship's AIS signal comes and goes, but it appears that Mermaid Sapphire (mother ship of Deepsea Challenger) is currently holding station off Ulithi atoll:

The lander-tender Barakuda has not shown up on AIS maps since shortly before the deep dive, as far as I know.

Investigators' Toolbox: More about timelines

I mentioned in the last post that timelines are a boon to reporters and investigators.

Timelines help evaluate the strength of assertions by interested parties, such as "Event A (his mistake) caused Event B (my crash)." Did A really happen before B? 

Timelines are only part of the picture, of course. Even if investigators confirm that Event A did happen before B, as claimed, and happened to the same machine, where's the proof that the first event led to the other? 

After most disasters, investigation turns up multiple causes -- errors and malfunctions -- that linked up over time, building to a system fracture. Knowing all the precursor events is important in preparing cautionary reports later. Here's a lessons-learned summary on the Piper Alpha rig blast, 20 years on.

Let's say evidence shows that the people in charge knew of a certain trouble report, and also knew that it put some of the mission goals in jeopardy. If they ordered that the mission proceed anyway, that tells us something important about the day-to-day priorities. The message: "It's safe enough for what I need. Get the job done, and then take the machine into the shop." 

That's the thinking that apparently led to the loss in 1968 of the nuclear submarine USS Scorpion and all her crew. The sub was supposed to get a safety overhaul in 1967, but Navy facilities were backed up so the sub went off to sea without the most important fixes indicated by the 1963 loss of the sub Thresher. The exact cause of Scorpion's loss has never been settled officially, but we do know from books like Silent Steel that it imploded as it went down, launching the aft end of the sub into the center of the pressure hull.

Timelines can take on a non-linear shape when the center of interest is moving. Here's one for the ValuJet 592 crash, from the NTSB report. It's a two-dimensional timeline of the DC-9's final moments, superimposed on an overhead view of the area.
 
Here's the same timeline with the third dimension added, reflecting changes in altitude.

A separate timeline would be needed to show the earlier string of errors and oversights, particularly those at ValuJet's contractor, SabreTech. This entirely avoidable crash (due to the ignition of boxes of old oxygen canisters carried in the cargo compartment) claimed all 110 souls. 

From the NTSB's report on the inflight breakup of TWA Flight 800, here's a different kind of timeline that conveys how the B-747 airframe broke up into three  sections, each taking its own trajectory. 

Timelines on the Web are more interactive than ever. Using the online tool Dipity, Mother Jones magazine assembled this timeline to organize information about a long string of events centered on the Deepwater Horizon blowout. Here's a sample screenshot:

To be useful in unraveling the root causes, all events on a timeline must share a common time base. It may seem easy -- "Just look at the clock!" -- but sequencing evidence from multiple sources can take a great deal of work. 

It used to be even harder. After Titanic sunk, landlubbing readers of the British and American findings may have been surprised to learn the logs provided by the vessels did not share a common time base.

In other words, an event that all the ships experienced simultaneously -- a specific CQD from Titanic's wireless operators -- wouldn't have been entered in the ships' log books as having happened at the same hour and minute, even if all ships were in the same time zone. The ships (including Titanic) reset their clocks to local noon each day, and local noon changes as ships go 'round the globe.

See this paper on Encyclopedia Titanica, "Titanic's Time Enigmas," for a detailed analysis of all the time reports (including the thorough logs kept by Cape Race) and a conclusion on what happened when. 

Long before the Internet and cellphones linked us to atomic clocks, the best I could do when setting our house clocks was to tune to a WWV on our shortwaveradio. WWV counted down to the correct time each minute.

Synchronization problems can still arise. Some eyewitnesses might not have noted the time at all. Land line phone calls aren't time stamped, unless the caller happens to phoning 911 or somebody on a cellphone.

If a witness with a 1990's-era video camera records a view of something falling off a plane at an air show, the time stamped on the tape won't be as accurate as if the witness used the camera on her smartphone instead. (That's assuming the user didn't try to set the time herself. By default, cellphones draw on network time to stamp phone calls and text messages; in that respect, we're all carrying around atomic clocks.)

So this reminder to drivers who are tempted to correspond while at the wheel, defying common sense and repeated warnings from the National Transportation Safety Board: after an accident, the police can use network records to prove you were texting at the time of the crash. So don't do it!