There's still half an hour before take-off, why can't I get on the plane?

When traveling by plane, many airlines recommend that passengers arrive at the airport to check in 2 hours in advance. Some international flights even recommend that passengers arrive 3 hours in advance.

China Southern Airlines boarding reminder information, the picture is taken from China Southern Airlines official website

Once you miss the check-in time, even if you have arrived at the airport and are confident that you can arrive at the cabin gate before the plane takes off, the airport will not make any concessions.

This is not because the airport or the airline is ruthless, but because there is a lot of preparation before the plane takes off, and some steps can only be carried out after the number of passengers and luggage is determined.

Important "Manifest"

Regarding this question, I first consulted pilots and flight attendants from two airlines around me. Although the pilots and flight attendants have different preparations to make before takeoff, their answers all point to the same important thing - the manifest .

The pilot needs to enter the data on the manifest into the computer on the aircraft, and only with the manifest can he apply for takeoff from the tower and then line up for takeoff according to the instructions.

There is a key step in the process of making the manifest, which requires the airline or the airport's loading department to calculate the aircraft's load balance based on information such as the aircraft model, flight fuel consumption, number of passengers (weight), luggage weight, etc., to keep the aircraft's center of gravity within a safe range.

Therefore, this step can only be carried out when the weight of passengers and luggage is completely determined. If more passengers continue to board the plane, the passenger weight and luggage weight will change, and the aircraft's load balance will need to be recalculated.

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Therefore, check-in is not allowed 30 minutes (or even longer) before the flight takes off, otherwise it will delay the journey of other passengers.

Load balance and center of gravity cannot be ignored

Although passengers don't have much physical sense of "load balance" and "center of gravity" when flying on an airplane, they are very important to the flight safety.

For example, the China Northern Airlines Flight 6136 crash in 2002 (also known as the May 7th Air Crash) was related to the change in the aircraft's center of gravity.

The cause of this air crash was arson . After the cabin of the plane caught fire, it could still fly for a distance. In this emergency situation, the pilot decided to avoid densely populated urban areas and make an emergency landing on the sea to avoid casualties on the ground. However, after the cabin caught fire, the passengers instinctively rushed to the front of the cabin where the fire had not spread, which caused the center of gravity of the plane to suddenly move forward, and the plane crashed headfirst into the sea.

In addition, in 2013, National Airlines Flight 102 suffered a tragic accident in which the cargo in the hold was not securely secured and moved during the flight, causing the center of gravity of the entire aircraft to shift backwards, resulting in the tragedy of the plane being destroyed and people dying.

According to a 2016 study, 77% of flight accidents are related to the aircraft's center of gravity being outside the safe range, and 57% of these accidents result in fatal consequences.

Since load balance and center of gravity are so important to flight safety, it is very necessary to allow staff sufficient time to make calculations and properly arrange luggage, fuel, and place counterweight loads.

By the way, when purchasing air tickets, if the plane is not full, the airline will not allow passengers to choose seats completely freely to avoid the situation where all passengers choose one side of the plane, or are concentrated in the front or back of the plane.

Moreover , during the flight, even if the front seat is empty, the crew will not allow passengers to change seats at will.

For example, in 2015, there was an incident where a passenger did not sit according to the seat on his ticket and insisted on changing to a seat closer to the front, which caused other passengers to follow suit and ultimately affected the load balance of the aircraft.

How do passengers know their weight if they don’t weigh themselves?

Since load balance is so important, how do the crew know the weight of us and our luggage? After all, when boarding, only checked luggage will be weighed, and people and carry-on luggage will not be weighed.

The answer is simple: it depends on estimation. Although load balance and center of gravity are important, they do not need to be exact.

According to the classification in the "Aircraft Weight and Balance Control Regulations" of the Civil Aviation Administration of China, most of the flights we take are "large cabin aircraft".

For this type of aircraft, the "standard average weight" of passengers and luggage can be used for estimation. Because the larger the aircraft and the more passengers there are, the more accurate the result of using the standard average weight will be.

Aircraft weight and balance control regulations

For example, the standard average weight for an adult is 75 kg, including clothing and hand luggage, while the average weight for a child is 38 kg and for an infant is 10 kg.

The provisions of the Standard Average Passenger Weight in the Aircraft Weight and Balance Control Regulations

Of course, the "standard average passenger weight" used in my country may not be applicable in other countries and regions. For example, according to the data from the Centers for Disease Control and Prevention (CDC), the average weight of adult males in the United States is 90.63 kg (199.8 lbs), and that of females is 77.47 kg (170.8 lbs). Adding the weight of clothing and luggage, the average weight is far more than 75 kg.

In addition, some airlines have set limits on the size and weight of carry-on luggage , on the one hand to ensure that the luggage can be placed in the luggage rack in the cabin, and on the other hand to prevent passengers from carrying too heavy luggage, which will affect the weight estimation.

Last minute limit

Although check-in stops 30 minutes to 1 hour before departure, some special circumstances may occur.

For example, some passengers who have completed check-in may be so absorbed in shopping in the duty-free shops at the airport that they fail to reach the boarding gate before the plane door closes.

When the boarding gate is about to close, the names of these passengers will be announced at the airport as a reminder. However, if they still fail to arrive after the announcement, the captain has the right to order direct takeoff, after all, it is impossible to let the entire plane of passengers wait.

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In this case, the aircraft does not necessarily need to be re-weighted and balanced.

There is a term called "last minute correction", which means that after the manifest is made and before take-off, the flight can make minor adjustments to the load without re-making the manifest , including adjustments to fuel weight, crew, passenger personnel, and cargo, etc.

This adjustment only needs to be filled in the remarks column of the manifest, and the captain and the relevant personnel responsible for load and balance need to confirm, verify and sign.

For example, the following figure is a "last minute correction" table on an airline's manifest. The values ​​that can be adjusted in the last minute correction are related to the maximum no-fuel weight, maximum takeoff weight, and maximum landing weight.

The "last minute amendment" section of an airline's manifest

This manifest is for the A320-200 model, and can adjust up to 6 passengers or 500 kg of load. If the number of people or load is changed too much, it is still necessary to recalculate the load balance and re-make the manifest. This will undoubtedly delay the time of other passengers on the flight, so don't forget to board the plane in time after checking in.

In addition, there is a detail worth noting when communicating with the pilot: if all personnel are present, cargo is loaded, the aircraft door is closed, and there are no restrictions on the route, you can apply for early takeoff. Although there are a lot of prerequisites, you may be able to catch up!

Finally, I would like to remind you again that it is best to arrive at the airport as early as possible when traveling by plane, and pay attention to the boarding time after checking in. This will not only ensure a smooth journey for yourself, but also show respect for other passengers and crew members.

References

[1] China Civil Aviation Network: What is an aircraft manifest? What does it contain?

https://www.ccaonline.cn/hqtx/906692.html

[2] Civil Aviation Administration of China: Regulations on Aircraft Weight and Balance Control

http://www.caac.gov.cn/XXGK/XXGK/GFXWJ/201911/P020191104349057958745.pdf

[3] Boyd D D. General aviation accidents related to exceedance of airplane weight/center of gravity limits[J]. Accident Analysis & Prevention, 2016, 91: 19-23.

[4] https://www.cdc.gov/nchs/fastats/body-measurements.htm

[5]https://m.thepaper.cn/newsDetail_forward_1348130?commTag=true

Planning and production

Author: Science Scraps Popular Science Writer

Reviewer: Wang Zijia, Professor of Transportation Engineering, Beijing Jiaotong University

Planning丨Yinuo

Editor: Yinuo

Proofread by Xu Lai and Lin Lin

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