How cabin connectivity can reduce interference

I know the topic sounds rather outrageous, but just think of it for a minute.

Imagine yourself being inside an aircraft taxiing towards the runway when the captain comes on the P/A and says that someone has left his/her mobile phone on and that he is not able to use the weather radar because of the interference and asks everyone to make sure their phones are switched off. Not long after, the flight attendants patrol the cabin and found the guilty passenger, a stern argument occur between the flight attendant and the passenger until the passenger yielded.

Such a scene isn't exactly unusual since the early days when mobile phones became everyone's essential communications device, and with the second mobile revolution, the smart devices, passengers feel even more attached to their devices and their need to connect with the world.

Now while the Captain of the flight is probably making it up about not being able to use the weather radar, let's imagine another scene:

The crew of a company with a fleet of corporate jets noted unusual problems with its ADF receiver on approach several times. On one trip, one of the pilots determined that the ADF receiver was affected whenever the CEO powered up his Blackberry just prior to landing, to see if he had any emails about his meeting appointment and the arrangements made between his landing and the appointments.

Now, this second story isn't fiction. The crew couldn't do much to the CEO who signs their pay checks, but it got to a point when they were on an NDB approach to an airport in low overcast condition when the CEO switched on his Blackberry again, and the ADF receiver deflected immediately. The Captain, the company chief pilot, immediately executed a missed approach, climbed to 10,000ft, went to the cabin, and demanded that the Blackberry be surrendered, citing that had the First Officer not been watching the ADF when the Blackberry was switched on, the aircraft would have lined up with anything other than the runway. He didn't let the CEO have the Blackberry again until the engines were shutdown after landing, and refused to start the engines without the CEO's Blackberry in his hand for every single remaining flight of the trip.

We all know that the problem is not the mobile phone specifications, but phones that are out of specs. Consumer electronics are unlike aviation electronics as they are not tested individually to ensure they are not making haywire electromagnetic emissions which can interfere with other aircraft equipment.

In that business jet case, the CEO got a new Blackberry, and the old one was tested and found to have problems. When it couldn't latch on to a cell tower, it started its powerful search, which unfortunately for that phone and the crew on that day, the phone started to emit radio signals in frequencies it should not have, with quite some power.

The company ended up having to test all electronic devices used by the CEO and division presidents, and those that failed, were sent back to the manufacturer. This company seems to have had bad luck with 2 - 3% of the devices failing the tests, although the person that provided the story suspects the number would generally be lower.

It would be very expensive to get consumer devices to be certified for use on airplanes. We've seen that banning use of these devices is in many cases a losing battle. We've also seen many cases of interference during approaches that couldn't be repeated in the lab. I've heard of cases of airplanes being thrown off the ILS due to cellphone interference. But note the trend there... most if not all of this occur at low altitudes. At high altitude, I haven't heard of any disturbing cases, either because the interference there is not there, or doesn't affect aircraft equipment other than the crew hearing an annoying rapid pulses on their radios.

So, why am I saying that cabin connectivity can reduce interference?

There are two main points:

1. Inducing devices to emit at low energy

Most of the interference problems from cellular devices are caused by high powered transmissions in search for a tower, or the struggle for the device to latch on to a cell tower. Installing picocells in airplanes connected to the ground through Air-To-Ground datalink or SatCom datalink, can allow the phones to be connected to a cell "tower" at low energy, which reduces or even eliminates stray radio frequency transmissions from these devices.

So providing for connectivity, can already reduce stray RF interference from onboard cellular devices.

But this doesn't always solve interference at low levels on its own. When you give a cellular device a choice of two signal sources of equally strong cellular towers, which one would it choose? Once the airplane goes to lower levels, the risk of cellular devices from latching onto a cell tower on the ground increase... and the lower the airplane goes, the more dangerous interference becomes. At this point, we must rely on the next benefit.

2. Induce the willingness to switch off and wait

The willingness of people to switch off their devices when they're told to depends on the time they have to wait until they can switch it on again and connect. The shorter the wait, the more willing they are.

I, like many people, is addicted to being connected. I hate having to switch my devices off, but as a passenger, it is my duty to do so. But not all people are willing to switch it off. Many still push their lucks by remaining connected to the very last moment such as the aircraft commencing the take off roll, or switch the devices on while the aircraft is still rolling down the runway on landing.

Since airlines begin to allow devices to be switched on on airplane mode, I was happy to comply and switch it off as soon as I sat down and buckled up and then switch it back on in airplane mode as we passed 10,000ft... that was until I had 3G connection (yes, I'm hooked). So at times, I must admit, that I've joined the "push your luck" crowd (and been caught a few times!)

But I honestly believe, if I can switch my device back on and connect as soon as I've passed 10,000ft, I would no longer join the violators and the "push your luck" crowd". I've only enjoyed 1 flight with connectivity on board, and I was willing to switch my phone off as soon as we pushed back, because I know I can connect again in less than an hour.

The cause of Saudi Arabian's connectivity with OnAir has gone a different way. With many people forgetting to switch their phones off, they resorted to keeping the picocells active at all times even in the ground and when the aircraft is at low level. Not only does it reduce interference, it allowed them to remind passengers through a cell or sms broadcast that they forgot to switch their phones off (and advertise their service too of course).

So, let's get back to the two points:

1. Inducing devices to emit at low energy

2. Induce the willingness to switch off and wait

Both, need the aircraft to be connected.

Now back to the business jet story... At the end of the day, the company decided to install connectivity onboard its corporate jets. Although it is unclear whether it is WiFi only or include GPRS service, but one can safely guess that those two points work. Now, has anyone with connectivity onboard ended up with more interference problems during approaches? I guess not.