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Episode 49: Cellphones on Planes and Helium Raft

  • Cell phones disrupt airplane navigation: mythbusted. Modern planes are well-shielded enough to not be affected
  • Flying helium raft: mythbusted. The raft would be much too large and flimsy

Adam, Jamie and Kari built a gigantic raft filled with helium to see if they could make Adam fly. Things didn't turn out as well as they would have liked, but any episode that starts with Adam hanging upside down in a net, looking like he got caught in a trap from Lost, was plenty of entertainment even if the busting wasn't done as well as it could have been.

Grant, Tory, and Kari handled the construction of a mock cockpit to see if cell phones could disrupt the navigational equipment. They eventually upgraded to a Hawker 800XP corporate jet, which they were unable to cause any interference with. Their busting showed that interference was possible, but only if the wiring wasn't properly shielded.

Cell Phones & Planes

Myth: The reason that you can't use your cellphone on an airplane is not because it will interfere with the in-flight instruments but because it forces you to use the in-flight phone on the back of your seat.

Background info (thanks Mattfn and peastham of the MBFC):

In-flight phones work in one of two ways. Over land they send signals to one of 135 land-based radio towers. Over the water, they send their signal up to a satellite. Hence, they are fairly expensive.

The build team had two theories as to how this myth might be true:

  1. The cellphone signal masks or blocks the radio signal from the airport
  2. The cellphone signal affects the navigation equipment directly

Setup

The testing for this myth was a bit interesting as it is illegal to take a switched-on cellphone into an airborne plane. They tried to get a commercial airline, chartered airline, anything, but Federal law messed up their plans. That meant that the MythBusters had to build a mock cockpit for them to test with on the ground. Grant and Tory picked up a laundry list of components from Faeth Aircraft in Sacramento, including a gyro stabilized magnetic compass system, VHF communication transceiver, navigation receiver / VOR navigation system, and GPS. Jeff Gutow, aerospace engineer, assembled their mock cockpit. After they raised an antenna above the roof of M5, they were able to get a signal from San Francisco's VOR navigation station.

The test equipment consisted of:

  • Anritsu MS2721A spectrum analyzer to measure the signal given off by the cellphone.
  • Faraday cage inside of a freight container to make sure their were no stray signals being measured.
  • A Ramp tester to simulate the signal from the airport
  • Signal generator was used instead of an actual cellphone, so that they would be able to adjust the amount of power in the signal to see how much power it would take in order to disrupt the navigation.
  • VOR navigation gauge: they monitored the deflection of the needle on the gauge to see if it was being interfered with by the cellphone.

Testing inside of the Faraday cage

They first tested out their spectrum analyzer with a CD player, iPod mini, and a portable game, all of which barely registered on the spectrum analyzer. A cellphone, however, showed up as a big spike.

Next, Grant monitored the needle on the VOR navigation system while he simulated various cellphone signals. The GSM signal showed no needle deflection, even when amplified 1000x. A 800Mhz signal, however, showed major needle deflection, as did 850Mhz and 900Mhz signal. This showed that it was possible in theory to interfere with the navigational equipment, but their wiring wasn't shielded in the same manner that an airplane would have been.

Moving cockpit test

They concocted a setup where their mock cockpit was mounted in the pack of a pickup truck and driven around in a parking lot near the airport. They felt that a moving cockpit receiving a signal from an actual navigation station signal would be more accurate. Unfortunately for them, their mock cockpit didn't seem to like their setup -- even with the signal generator off the navigation system was going haywire.

Hawker 800XP tests

They switched to a real plane, a Hawker 800XP provided by Tom Benvenuto, VP Flight Operations, Sunset Aviation. The 800XP is a plush 8-person corporate jet filled with top-of-the-line LCD electronics. Benvenuto made the point that the electronics on the aircraft were very well-shielded, so it should be much more resistant to interference than the MythBusters mock cockpit. Even though they couldn't fly the plane while testing due to legal issues, they were able to test with the plane on the ground.

Grant started off with the 800Mhz signal that caused problems in the Faraday cage test. There was no interference with the 800Mhz signal or any other signal they tested.

busted The final explanation is that, even though the airplanes appear to be well-shielded against cellphone interference, there are so many different electronics in a cockpit, as well as so many different cellphones constantly coming out, the FAA doesn't want to do the necessary testing.

Helium Raft

Myth: If you fill a raft with helium, you can fly on that raft

"This wins as the strangest position I have ever been in on this show." - Adam

"Don't you love how he qualifies it with, 'on this show'?" - Kari

Previously: * Lawn Chair myth * Helium Football myth

Test 1: Inflated dingy

They inflated a small dingy (raft) with helium to see if it would fly. They first filled it with air and measured the volume, which was 20.5 cu ft. Then they refilled it with helium to see how much weight it would lose. The helium-filled raft gained 4 lbs of buoyancy -- nowhere near enough to fly even by itself.

Test 2: Airline life raft

They figured that filling up a larger raft may get them closer to liftoff, so they tried out a 25 ft. diameter life raft. The helium-filled raft lost 1/4 of it's weight -- about 60 lbs. It still wasn't enough for liftoff.

Test 3: Escape slide raft

They next tried the escape slide raft (last seen in the Escape Slide Parachute Myth, which can hold 325 cu ft of helium. The escape slide lost about 40 lbs but still weighed 121 lbs -- no liftoff.

The math

It takes 16 cu ft of helium to lift 1 pound. In order to lift 300 lbs (200 lb Jamie/Adam plus a 100 lb raft), it would 5000 cu ft of helium, which is approximately 1/3 the cabin size of a DC-9 airplane. For reference, the Hindenburg carried 7,000,000 cu ft of hydrogen.

Massive pontoon raft

Given the need to build a raft for 5000 cu ft of helium, they decided to make pontoons out of heat-sealed polytubing, which is a clear plastic tubing used to transport A/C around a movie set. Their 50 ft test pontoon had 5 lbs of buoyancy -- a little bit less when you consider the tape to hold together the tubes -- which means that it would take 40-50 tubes in order to lift Jamie or Adam.

The final raft design: * 2500 ft of plastic tubing * 2 tiers of 25 pontoons each, set cross-wise to each other * packing tape at 10 ft intervals to stitch the pontoons together * silicon caulk and zip ties to seal each tube * water jugs to use as ballast * netting across the top of the pontoons

Prophetically, back at M5 Adam declared, "It's looking to be nigh impossible to pull this off"

They used what appears to be a hanger at Alameda to assemble their gigantic raft. It took took two days to construct and used up 36 cylinders of helium. Adam and Jamie weren't very thrilled with the difficult build:

"Once in every generation a myth comes along that does not thrill us" - Adam (in helium voice)

"This is strange, I have never seen anything like this before" - Jamie

"It has to be the single largest thing I have ever built, bar none, let alone in two days" - Adam

Adam was, however, happy with his outfit:

"This is my new toy, my new SWAT team tactical black climbing harness. My sister gave it to me. My whole family is like this." - Adam

"I'm wearing the wetsuit because it makes me look good, damn good." - Adam

Adam, in black SWAT team tactical climbing harness and wetsuit, was lowered onto a mini-raft on top of the massive raft. They started cutting the ballast on the raft, but one part of the raft started raising too quickly, sliding Adam off his mini raft, down between the pontoons, until he was hanging beneath the raft hanging inside of the netting they had spread across the raft.

Jamie: "Hey Adam"
Adam: "Yeah"
Jamie: "This isn't working"
Adam: "No, it seems to have failed utterly"
Jamie: "You've liked slipped right through to the bottom side"
Adam: "I feel like something that got cut out of The Matrix here."
Jamie: "Are you alright"?
Adam: "I'm fine. I'm upside down and I'm in a net and I'm below the biggest thing ever built out of helium and balloons, but I'm fine."

Adam was cut out of the net and then started taking a knife to the helium pontoons. A very high-pitched Kari declared, "Oh my god, we might need to open a door. It's getting kind of weird."

A very tired/frustrated Adam declared this one busted. A raft would have to be too big and unwieldily to lift a person.

Comments

i think the myth budsters should make the raft bigger and do what ever it takes to lift them off the ground

I am a private pilot with many hours in a CRJ 200 simulator and have used my cell phone in the air many times and have never detected a navigational problem, granted my navigation system is not as complex as the one on a large jet. We have never had trouble with phones on in the simulator. I heard if a cell phone is broken in that it admitts an abnormal signal, it could interfere. There are many strange problems that accure in flight to onboard sytems such as a complete rebooting of the FMC (flight management computer) or autopilots doing strange thing that are not explained but luckly pilots have been able to take manual control even if it ment fighting the controls.

The reason the FAA mandates that cell phones be turned off prior to taxi/takeoff is because of an emercency. The first and last stages of any flight is the most critical. If anything happens, we (the crew) want your utmost attention. Also, Allthough cell phones do not appear to cause Navigation problems, they can sometimes cause excess static communication noise through our headsets. This is more common on small planes though.

The reason phones are not allowed in planes is because they interfere with nearby cell towers. 200 phones or so per plane rapidly switching from tower to tower would overload the cell network.

We are having a discousion on Google+ about this,... I am of the view that if the FAA has not outlawed Devises on personal civilian aircraft here is no real reason except financial reasons,...