Explainer Mailbag: Explainer Asks, Readers Tell

Explainer’s colleague The Earthling has theorized that humankind functions like a global brain. To hell with theory, Explainer proves it! After Explainer posed questions about this week’s events, Slate readers went to work, as did Slate and other news sources. We haven’t gotten all the answers, but it’s a start.

1. Why can you turn off a transponder?

Some readers thought Explainer wanted to know why terrorists would want to turn off a transponder, but most realized that the question referred to why the devices are configured to allow non-homicidal pilots to do such a thing. Reader James Iry might have put it best:

“Two reasons. The first is that on the ground it’s useless and just generates more noise for the air traffic control system to sort out. The second is that it can malfunction.  A misbehaving transponder might broadcast continually, send an incorrect altitude, or send the wrong code. In any of these cases it’s probably better to send no signal at all than send a bad signal. Giving the pilot the ability to turn off a transponder is really just nod in the direction of Murphy.”

2. Can you turn off a plane’s cockpit voice recorder or flight data recorder?

Yes. The Christian Science Monitor interviewed the air traffic controllers who dealt with Flight 11. One of them “speculates that anyone knowledgeable enough to cut off the transponder might also have pulled the circuit breaker for the cockpit voice recorder in the so-called black box, deactivating it, to minimize information available to authorities.” And Slate reader Ken Shirriff referred Explainer to thisAviation Week article about the 1997 SilkAir crash of a 737. In that crash, U.S. officials suspect that the pilot activated the circuit breaker to cut power to both recorders.

3. What rules govern when a president can prohibit congressional intelligence briefings?

Explainer is still working on this one, but the Chicago Tribune reports that Sen. John McCain, R-Ariz., says the Bush administration’s briefings have become gradually less informative over the past few days. McCain (who’s not complaining) says he receives “much less information than I do from turning on the television set.” Sen. Dick Durbin, D-Ill., goes further, calling the briefings “a colossal waste of time.” Explainer recommends they address their thank-you notes to Sen. Orrin Hatch, R-Utah.

3. Cell phones work on airplanes? Why does the FAA discourage their use? What’s the maximum altitude at which a cell phone will work?

From this morning’s New York Times: “According to industry experts, it is possible to use cell phones with varying success during the ascent and descent of commercial airline flights, although the difficulty of maintaining a signal appears to increase as planes gain altitude. Some older phones, which have stronger transmitters and operate on analog networks, can be used at a maximum altitude of 10 miles, while phones on newer digital systems can work at altitudes of 5 to 6 miles. A typical airline cruising altitude would be 35,000 feet, or about 6.6 miles.”

The Times added that “there is little evidence, if indeed any, to suggest that the use of cell phones interferes with an aircraft’s avionics or communications systems. In other words, no one knows with certainty whether cell phones affect an aircraft’s ability to communicate with ground personnel or other aircraft. After all, an abundance of radio, television and other communications signals already travel through airwaves with minimal consequences for airborne communications systems.” Ken Shirriff (again) referred Explainer to this 1999 Wall StreetJournal article, which concurs with the Times’ judgment.

4. How long were the markets suspended during the Great Depression, and why?

Shaula Massena mailed in a link to this ABC News story. Fun facts to know and tell: “Since 1885, the New York Stock Exchange has closed more than four dozen times for various reasons, including presidential funerals, the armistice that ended World War I and for the lunar exploration on July 21, 1969.

“But even a two-day closure is rare. The last time the NYSE closed it doors for two days was for a much happier occasion, on Aug. 15 and 16, 1945, to commemorate V-J Day, the celebration of the Allied victory over Japan that ended World War II. The last time the exchange was closed for a week was in March 1933, when President Franklin Delano Roosevelt called for a nationwide bank holiday.

“More recently, the NYSE closed for a day and a half in the wake of John F. Kennedy’s assassination. The exchange closed at 2:07 p.m. the day Kennedy was shot – Friday, Nov. 22, 1963–and closed the following Monday for the slain president’s funeral.

“Weather conditions have also been known to keep the exchange closed, such as Feb. 10, 1969, when heavy snow closed the exchange, leaving it to open late the next morning at 11 a.m. The NYSE also closed during New York City’s blackout on July 14, 1977.

“Perhaps the longest stretch of time the exchange has ever been closed was from July 31 to Nov. 28, 1914, pending the outbreak of World War I. Trading in bonds with price restrictions reconvened on Nov. 28 that year, with trading in a limited number of stocks under price restrictions on Dec. 15. All restrictions were removed from trading on April 1, 1915.”

5. Can a plane’s black box survive a jet fuel fire? If so, why isn’t everything made out of the same stuff?

Cecil “The Straight Dope” Adams answered these questions in 1996, multiple readers noted. Click here for his answers. For more on black boxes, read thisScientific American column or go to HowStuffWorks.com.

6. Can Congress declare war against an individual or group?

Slate’s Dahlia Lithwick answers this question here. (Short answer: Yes.)

7. Will Sept. 11 be remembered as the deadliest day in American history?

We don’t know the death toll from Sept. 11 yet, but Ken Shirriff (yes, him again) refers readers to this CNN story, which notes that 6,603 American forces were killed in battle on D-Day. And reader Garry Jaffe notes that more than 12,000 Americans died during the Battle of Okinawa.

  Next question?