Just when does that light go on?

[timmcat]

Just wondered, flying through a bit of chop on the cruise the other week, what constitutes the seat belt lights to go on? As a fairly inexperienced flyer, I am sure I have been asked to fasten by belt in calmer conditions. Is there a set criteria, or is it the experience of the crew and / or weather radar that gets us to belt up?

[shlittlenellie]

In 'AUTO' the signs illuminate whenever the flaps are extended. Hence, after takeoff, the belts go off when the flaps are fully retracted. Similarly, on approach, the seatbelt signs would go on when the flaps begin to extend. However, most carriers will manually illuminate the signs on passing through an altitude in the descent; often 10,000'. Many operators will have the signs 'ON' for takeoff and manually switch them off when safely airborne, this keeps control of the cabin since if there were to be an engine failure/fire and a rapid return to airport of departure, the last thing we want is for the seatbelt signs to go off as we retract the flaps.

In turbulence, the signs will be turned on manually. This is subjective and in light-chop this will be done in consultation with the cabin crew who can report on what services are being carried out in the cabin and the levels of turbulence in the cabin.

[pvdmeij]

I know a captain of a 747 who has a (movable) set of false teeth on this glareshield. If they start rattling he swithes on the fasten seatbelt sign. :D
But indeed the length of the plane affects the wellbeeing of the passengers in the rear very much.Better be safe than sorry.

[Flap 5]

Weather radar will give some indication, especially at night, although it detects precipitation and not turbulence. Othwerwise it is completely down to the Captain. Some will turn the signs on at the slightest turbulence while others will allow a slight chop without turning on the signs. Myself I have been on many long flights with the signs turned on in just light chop and have the seen the inconvenience this causes passengers. Therefore when I am the Captain I tend to leave them off in light chop. You have to be careful though in our litigious society. Although now if you leave them on too long someone will complain of the onset of deep vein thrombosis!

[GearUp CheerUp]

Can be a difficult call. You start to get a bit of light chop and think it'l probably cease then it gets worse so you put the seat belt sign on. After a couple of minutes the purser comes forward to give the cabin secure signal and then the ride becomes totally smooth again. So you turn the belts off and the turbulence starts again.

Not for nothing is the seat belt switch often called the turbulence switch ;-)

[Captain Airclues]

On the 747-400, with the seatbelts selected to 'Auto', the signs will be on whenever the aircraft is below 10,300ft. However, we switch them on manually when we have 20 minutes to go before landing, to give the cabin crew time to secure the cabin.
Before departure we plot our route on a 'Significant Weather' chart, which shows areas of cloud and turbulence, as well as winds and temperatures. The weather radar is used to detect areas of precipitation, and the tilt is used to estimate the vertical extent of the cloud, and hence the possibility of turbulence.
During the cruise we are often warned about impending turbulence by ATC, particularly in the USA and Canada. We have an air-to-air frequency in some parts of the world, where crews can warn each other of problems, or ask for advice. Although you cannot always rely on the weather charts, if an aircraft 100 miles ahead of you at your level reports turbulence, you can be pretty sure that you will get it as well.
We also keep an eye on the wind and temperature, compared with the forecasts. A rapidly changing wind or twmperature can cause turbulence, so it is possible to anticipate this, and switch the signs on.
A combination of high ground and strong hinds can also make life uncomfortable so it is worth checking the safety heights in strong wind conditions.
We also work closely with the cabin crew, briefing them before flight about any likely areas of turbulence, and keeping them informed about any ATC or pilot reports. It is important for us to know the progress of the meal service, just in case the situation gets worse. As well as protecting the passengers, we are also concerned about the safety of the crew, and the meal service situation will affect the amount of warning that the crew need to get things stowed away.
It isn't possible to get it right all the time. Sometimes you just have to rely on that old feeling in the gut, otherwise known as experience.
Hope this helps.

Airclues

[SkyCruiser]

Hi Airclues, how are you?
:p :p :p :p

[PAXboy]

GearUp CheerUp: Exactly what happens, when the lights come on - I know that we are through the worst of it!!!

The equator is one of the obvious places for turbulence. There is activity there all year round. In just under four weeks time, I shall be going down to JNB again and if I watch the Sky Map, I can almost predict when the chop will start.

During a flight deck visit on one such trip, I asked about the 'threshold' for strapping us in and the Capt replied, "Being up here, we get bounced around a lot more than you do. If it is getting uncomfortable for us, we know it's getting bad for you."

[Dockjock]

In North America, the practice of giving "ride reports" is very common. When an aircraft is checking onto a new centre frequency the call will often be "Good morning Toronto AC345 FL350 light chop" and so on for subsequent aircraft. The controller can then get an idea of which altitudes are smooth, and which are bumpy and generally where the best ride is.

Subsequent crews on check-in to a new frequency (especially if experiencing turbulence) will often say "any ride reports?" and the controller can suggest alternate altitudes.

When the frequency is very busy, this practice is frowned upon, but when time permits everybody benefits from a better ride!

[timmcat]

Many thanks for the info everyone, much appreciated... think I'll just keep it fastened all the time (as recommended)!

[A Very Civil Pilot]

Just flown as a pax on Malaysian. Seat belt signs on and off throughout the flight, but just as many pax wandering about when on as when off. CC didn't seem too concerned.

[scanscanscan]

Rumour was...And I believe I read that... A Thia Airways Captain years ago did not have the seat belt sign on, and a European, first class, male busines man, hit the ceiling and then fell braking his back on the seat armrest.
The enroute emergency landing for his medical needs was then made in Istanbul.
The captain was arrested and jailed pending trial.
He was found guilty, as he did not have the seat belt sign on, when his weather brief chart showing CAT in the area was produced.
His plea that the flight was totally smooth, until, "Bamm" it hit them was not accepted as valid on the evidence of the weather brief chart.
I heard he was fined £70,000.00 which Thia Airways deducted from his pension fund, then fired him.
Balpa attended his trial which was accommodated between that of a prostitute and a crook.
Balpa observers clocked the judge falling asleep during the Captains trial.
This is all written up in the BALPA magazine and sure impressed upon me the seat belt sign way to go.
If I had them on and the folks wanted to ignore them well I was CYAed all the way.

[foxmoth]

Flown many times in the states wherethe signs go on at the LEAST sign of bumps (to cover their backs), fine,but then the pax just ignore the signs and NOT enforced by the cs as it is not worth the hassle in light turbulence. Much better in real life if you can use a sensible level of turbulence and have it backed up by the cs as most European operators do.