As authorities continue to search for the Malaysia Airlines jet that went missing on March 8, thoughts turn to air safety.
It's exceptionally rare for planes to experience malfunctions, especially serious ones. "Planes don't fall out of the sky at 36,000 feet," says CNN's aviation correspondent Richard Quest.
Even when errors do occur, most often human in nature, airlines and traffic controllers employ a vast array of procedures to ensure our safety.
Hong Kong Airlines was involved in nine incidents in which pilots apparently disregarded instructions from air traffic controllers (ATCs), including a plane taxiing onto a runway without permission and failure to follow instructions about altitude and direction.
Hong Kong's Civil Aviation Department is still investigating those incidents.
Other recent cases of miscommunication between pilots and ground controllers include:
• July 2010: The captain of an Air Blue flight disregards instructions from traffic control and crashes into mountains near Islamabad, killing 152.
• June 2013: Two Boeing 747s narrowly miss colliding over Scotland when one plane turns right and the other left -- effectively doing the opposite of ATC instructions.
• December 2013: A British Airways jumbo jet crashes into a building at Johannesburg airport when the pilot goes down the wrong taxiway.
According to Ady Dolan, an air traffic controller at London Heathrow Airport who spoke with CNN for this story, human errors between pilots and air traffic controllers occur on "a daily basis."
But while common, most errors go unnoticed and are of no threat to safety, thanks to established systems of communication and technology.
English ... but whose English?
According to Dolan, controllers at Heathrow deal with 85 airlines and 1,350 flights a day.
Controllers need to be able to communicate with pilots of many different nationalities, he says.
English is the language of aviation and vital for pilot-controller communication.
"We're lucky that English is the language of the air," says Dolan. "If English is not the pilot's first language and they only come to Heathrow occasionally, we need to afford extra care to that pilot.
"We can't speak with speed and abbreviation as we would to someone who comes here several times a day."
A pilot who often flies to China and Southeast Asia, and who spoke with CNN on condition of anonymity, says pilots and air traffic controllers generally enjoy a good relationship, especially in Hong Kong where ATC standards are high.
"But China can be a bit of an issue," he says. "We should all be speaking English, but for a lot of people it's their second language."
The pilot says airlines have varying policies on recruiting pilots with good English, and this can cause problems.
Patter and chatter
The International Civil Aviation Organization (ICAO), a United Nations agency that sets and regulates standards of air safety, says standardized phraseology is an important part of pilot-controller dialogue.
For example, before the 1977 KLM-Pan Am crash, the pilot reportedly told traffic control, "We are now at takeoff" as he moved down the runway.
The controller understood this to mean the plane was ready to take off, but was still stationary and waiting for further instructions.
For this reason the controller didn't warn the pilot about another plane on the runway, which was obscured by thick fog.
"Pilot and air traffic controller radiotelephony communication is an important part of training leading up to licensing for both functions," says an ICAO spokesperson. "ICAO guidance requires that both controllers and pilots use standardized phraseology in their communication exchanges.
"ICAO is continuously reviewing and updating its standardized phraseology guidelines to better meet the needs of the air transport system and ICAO language proficiency requirements have been in place since March 2008."
The relationship between controllers and pilots functions well generally, says South African Airways pilot Sarah Jones, who flies across South Africa and Africa.
"There are lots of structures in place to try and prevent miscommunication between us. Obviously, there has to be trust," she says.
While Jones says ATC standards are high in airports such as OR Tambo in Johannesburg, they're not as good at some other African airports.
She says it can be challenging when controllers and other pilots don't speak English.
"You have to be very vigilant, listening to the other traffic and having good situational awareness," she says. "It's an issue when they are speaking, say, French or Brazilian, and you can't understand what other pilots are telling ATC in airports where you would be more naturally cautious anyway."
Human error inevitable
Errors that occur as a result of pilot-controller misunderstandings are normal, but go largely unnoticed by passengers, according to the pilots and controllers interviewed for this story.
As air traffic increases, so does the potential for poor communication.
That's why it's important to have solid backup procedures in place, says Heathrow air traffic controller Ady Dolan.
Dolan works for UK-based NATS, a provider of air traffic services in the UK and more than 30 other countries.
The company also provides strategies for dealing with potential problems.
"At any airport if you have humans involved there are going to be errors," he says. "Our job as an ATC provider is to spot the potential for that error before it takes place and then when it does happen to have mitigations in place to correct that."
He says typical errors might be "simple," like a plane ending up facing south instead of north on a stand.