How many passengers are in planes in the air at any given time in the U.S.A.?

CLARIFY:
1. Is it OK to focus on standard commercial flights (ex. not military flighters, freight flights, etc.)? Yes.
2. Is it OK to exclude flights flying over the US to land in another country? Yes.
3. Assume that we are discussing pre-COVID times when flying was more normal? Yes.
EQUATION: # of passengers in planes = # of planes in sky * average # of passengers / plane

BREAKDOWN UNKNOWNS:

# OF PLANES IN SKY:

Total Airport Runways: Let's assume there are 3 types of airports.
1. Airport # of Airports # Runways on Average / Airport Total Runways
  Major 10 4 10 * 4 = 40
  Medium 20 2 20 * 2 = 40
  Small 100 1 100 * 1 = 100

# of Planes Flying throughout Day on 1 Runway:

Let's assume that planes arrive / leave the runway in the same manner across each airport type. We can split the flying behavior peak hours v. off peak hours.
Let's calculate the number of planes flying from an airport assuming it has 1 runway.

Type of Behavior	Time	Hours / Day	Description	# of Planes / Hour	Total Planes / Day on 1 Runway
Peak	6AM - 9 PM	15 hours / day	Plane flies every 5 min	60 minutes per hour / 5 minutes = 12 planes per hour	12 planes / hour * 15 hours = 180 planes / day during peak hours
Off Peak	9PM - 6AM	9 hours / day	Plane flies every 15 min	60 minutes per hour / 15 minutes = 4 planes per hour	4 planes per hour * 9 hours / day = 36 planes during off peak hours

Total # of Planes Flying throughout Day on All Runways:

Airport Type	# of Runways	Total Planes on Peak All Day	Total Planes Off Peak All Day	Total Planes / Day
Major	40	40 runways * 180 planes / day = 7200 planes	40 runways * 36 planes / day = 1440 planes	7200 + 1440 = 8640 planes per day
Medium	40	40 runways * 180 planes / day = 7200 planes	40 runways * 36 planes / day = 1440 planes	7200 + 1440 = 8640 planes per day
Small	100	100 runways * 180 planes / day = 18,000 planes	100 runways * 36 planes / day = 3600 planes	18,000 + 3600 = 21,600 planes per

Total Planes Flying all Day: 8640 planes + 8640 planes + 21,600 planes = 38,880 planes in day
Average Total Planes Flying Now:
1. Let's say of the 38,880 planes flying all day, the average flight is 3 hours - i.e. every 3 hours the planes land. There are 24 hours day / 3 hours flight = 8 intervals of planes flying and landing.
2. The average number of planes in the air at any moment is equivalent to average number of planes that took off during the last 3 hours.
3. At any point, there are 38,880 / 8 = 4860 planes in the sky now.

# PASSENGERS IN SKY OVER US FLYING OFF:
1. Let's assume the average commercial flight has 120 people.
2. Given that there are 4860 planes flying now, 4860 planes * 120 people / flight = 583,200 people in the sky at this minute over the US.

PM Team · Answer 3 · 2018-08-11T20:17:07+0000

The key to answering this estimation interview question is to think about what information you have (or can estimate), which can help you get to the answer. You need to be clear about your logic and assumptions, and be clear-minded enough to be able to sense-check the ultimate answer you arrive at.

First, I clarify the question – what is meant by “airplanes”? All planes, private jets, commercial flights only, military, fly-overs? And what is meant by “right now” – literally right this second? What is meant by “over the US”? Landmass only? Does this include ocean territory? What about Alaska and Hawaii?

I will assume that “airplanes” can be divided into four categories: commercial passenger, freight, small private and military. There will be other types (like charters and crop-dusters) but to simplify things I will leave them aside.

I assume that these flights are only those flying domestically or to an international destination (but still over the US). I will exclude planes flying over the US from one country to another.

I assume that “right this second” means 6.45pm.

I assume that “over the US” means over the landmass of the contiguous 48 states.

Then I look at each type of plane to look for drivers of the ultimate number.

For commercial passenger planes, I assume a good driver would be the number of airports in the USA. I assume there are:

10 giant airports
20 major airports
50 medium airports
100 small airports

Giant airports would have about 20 flights per hour taking off, 18 hours per day. So, about 360 flights per day. At any one time, perhaps 15 per cent of these flights would be in the air. I would assume that the average plane would contain 250 people. So, that’s 360 x 15% x 250 x 10 airports = 135 000 people.

Major airports would have about 10 flights per hour, 18 hours per day. Fifteen per cent would be in the air at any one time, with an average of 200 people on board. That’s 108 000 people.

Medium-sized airports would have about 10 flights per hour, 15 hours per day. Fifteen per cent would be in the air at any one time, with an average of 100 people on board. That’s 112 500 people.

Small airports would have about five flights per hour, 12 hours per day. Fifteen per cent would be in the air, with an average of 50 people on board. That’s 45 000 people.

Freight is trickier to estimate. I would estimate that there are an average of 100 cargo flights per major city in the US per day, and I’d estimate there are 200 major cities. Fifteen per cent of these flights would be in the air at any one time. They would have an average crew of five. That’s 15 000 people.

For small private planes, I’d say there is one private plane for every 500 head of population (300 million people), and that one per cent of these planes might be in the air at any one time, with an average of four people on board. That’s 600 000 x 1% x 4 = 24 000 people.

For military I am less sure. Let’s assume there are 10 000 military planes in the US (big and small). Let’s say five per cent are airborne at any one time with an average of 10 people aboard. That’s 5000 people.

Now I can add up all the people. The total equals 444 500 people in the air right now over the US.

To sense-check this, let me just divide by 200 (the average number on board a commercial airliner). That’s 2222 planes in the air, or 46 over each of the 48 states.

Hmm, this seems a bit on the high side, so I may have over-estimated somewhere. I can go back through my assumptions and calculations to see if I can trim the number a bit. However, I don’t think I’m far off.

peakyblinder · Answer 4 · 2022-02-24T15:29:54+0000

Clarifying questions

1. Number of flights in the air at any given point in time? Yes
2. Both international and domestic flights are included? Yes
3. Do we include military jets and other air transportations such as helicopters? No
4. We need to calculate number of flights flying over US continental main land? Yes

Assumptions

At least one international airport (which is the main airport) per state.
US main land 48 states (excluding Hawaii and Alaska)
Cost to Cost travel time (air) - 3 hours to 6 hours:
Average travel time over US continental main land - 4 hours
Every hour a flight is taking off from a gate or arriving.
Each flight (domestic/international) carries about 200 travelers

Calculation:

The calculation is predicated upon number of flights that a gate can serve and flights that are queued by runways with in the average travel time of lights over US continental main land.

Major states (California, NY, Texas, Florida) : Having 2 main airports and 2 supplementary air ports

Rest of the states : Having 1 main airports and 1 supplementary air ports

Each main air port : 50 gates

Each supplementary air port - 25 gates

(Case in point - JFK has 103, Boston Logon has 102)

Air ports (Major states) = 16 (8 + 8)

Airports in other 44 states = 88 (44 + 44)

Main air ports total = 52 (44 + 8)

Runways in main airports = 8

Total number of runways in major airports = 52 * 8 = 416

Supplementary airports total = 52 (44 + 8)

Runways in Supplementary airports = 4

Total number of runways in major airports = 52 * 4 = 208

Total number of runways = 624

From our initial assumption:

Average travel time over US continental main land - 4 hours

A runway can serve up to 4 flights in 4 hours.

Therefore number of flights that could be flying over the US continental main land = 4 * 624 = 2496 flights at any given time.

2496 * 200 = 499,200 travelers

peakyblinder · Answer 5 · 2022-02-24T15:03:01+0000

Clarifying questions

1. Number of flights in the air at any given point in time? Yes
2. Both international and domestic flights are included? Yes
3. Do we include military jets and other air transportations such as helicopters? No
4. We need to calculate number of flights flying over US continental main land? Yes

Assumptions

At least one international airport (which is the main airport) per state.
US main land 48 states (excluding Hawaii and Alaska)
Cost to Cost travel time (air) - 3 hours to 6 hours:
Average travel time over US continental main land - 4 hours
Every hour a flight is taking off from a gate or arriving.

Calculation:

The calculation is predicated upon number of flights that a gate can serve with in the average travel time of lights over US continental main land.

Major states (California, NY, Texas, Florida) : Having 2 main airports and 2 supplementary air ports

Rest of the states : Having 1 main airports and 1 supplementary air ports

Each main air port : 50 gates

Each supplementary air port - 25 gates

(Case in point - JFK has 103, Boston Logon has 102)

Air ports (Major states) = 16 (8 + 8)

Airports in other 44 states = 88 (44 + 44)

Main air ports total = 52 (44 + 8)

Supplementary air ports total = 52 (44 + 8)

Total main air port gates = 52 * 50 = 2600 gates

Total supplementary air port gates 52 * 25 = 1300 gates

Total gates = 3900 gates (~4000 gates)

From our initial assumption:

Average travel time over US continental main land - 4 hours

A gate can serve up to 4 flights in 4 hours.

Therefore number of flights that could be flying over the US continental main land = 4 * 3900 = 15,600 flights at any given time.

ian ray · Answer 6 · 2022-02-20T19:18:55+0000

I see a lot of answers focus on the top down approach by thinking about demand from population and number of airports. But airlines have inelastic supply (finite amount of planes) which they report publicly and unit economics are very important. So airlines will be interested in offering the most units at maximum capacity per plane.

So first clarifying the definitions:

Do we only want commercial flights or are private and military flights included?
Do we want to consider international flights that are leaving or entering the country or only domestic that will always be in the US airspace?
There are a significant number of flights during the day vs night. Meaning at any given time during the day time the numbers of passengers will be much different than at night. Do we want a separate calculation, average all times, or perhaps focus on just daytime flights?
When you say “given time” is that “per hour” or “per minute”?

I am going to suppose we want to know the average number of passengers on domestic commercial airline flights in US airspace at any given time during the day. For which we could calculate:

Avg passengers per plane X Avg planes an airline has flying at anytime during daytime hours X Number of domestic US airlines

Supply of planes by US airlines:

There are 4 major airlines in the US (Delta, American, United and Southwest) and then about 12 minor airlines. All of which publicly release the amount of planes in their fleet
There are different sizes of planes with different passenger capacity
- Large plane = 300 passengers
- Medium plane = 150 passengers
- Small plane = 75 passengers
Let’s assume a major airline has 800 planes and a minor airline has 100 planes, all of which have the following breakdown for their fleet: Large 50% of fleet, Medium 40%, Small 10%
And each flight is 95% full

For “any given time during the day”, we know that there are flights of many different lengths across multiple time zones, and planes need to taxi, load/unload, clean, refuel, etc. So let’s also assume the amount of planes an airline has flying at any given time during daytime hours to be 30% of their total fleet.

So we can calculate the number of passengers in the air for an airline to be the sumation of the 3 types of passenger planes in their fleet, which is

( Airline fleet x % of fleet x 30% in the air) x (95% capacity of plane)

For example, a major airline would have:

120 Large planes with 34,200 passengers in the air
96 Medium with 13,600
24 Small with 1,710
which is a total of 49,590 passengers in the air

So for all 4 major airlines, we would have 4x as many to get: 198,360 passengers currently in the air. And the same calculation would give us all 12 minor airlines having: 74,385 passengers in the air.

Therefore there are about 272,745 passengers in the air at any given time in the US for domestic commercial airlines

Gaurav Gupta · Answer 7 · 2021-07-28T20:03:52+0000

Posting my first ever answer on this platform and expecting feedback and comments from you all. This will surely help me in improving my skills and confidence.

I start this with few assumptions

1) Number of States in USA = 50
2) Each state has 10 airports, so i am taking total number of airports 50*10 = 500

3) Average Pessanger in any flight = 250 nos

4) Taking domestic & International passenger flights for this case

5) Flight duration >=60 min, so at any given time is span of 1 hour

Working :-

A	B	C	D	E	F
Airport type	% weightage	Airport count	Operational hours in a day	Time for each Takeoff + Landing (In Min)	Total Flight per day (Derived) F=CD60/E
Very Busy	5%	25	22	1	33,000
Avergae Busy	15%	75	16	5	14,400
Less Busy	80%	400	8	10	19,200
Total		500			66,600

So basis the assumption the followign are the outcomes

1) Approx 66K flights are landed or takeoff every day (F=C*D*60/E)

2) Average 9.9 hours is the operation time (sumproduct of B & D)

3) So 6727 unique flights are in the air in any given time

(Total flight/average operational hour) (66600/9.9)

So 1.68 Mn passengers are in the air at any given time

Unique flight in that hour* number of passenger (6727*250=1.68mn)

anonymous-1 · Answer 8 · 2021-06-19T23:22:48+0000

Clarifiying question:Are we referring to commercial airplanes only? Are we referring to this time means 7am EST? If the answer to above is yes then let's look at the problem:

Equation: Number of airplanes at any given point in US = Number of flights just took off from US + Number of flights landing in US + Number of flights flying in the US air

Assumptions:

1. There are 51 states in US and each state has approx on avg 10 cities. Each city might have one or 2 airports.

2. International airports: Avg of 3 in each state=151 airports

3. Domestic airports: Avg of 10 in each state=510 airports

International Airport:

International airports primarily operates during night hours and most of the flights take off during night and land in the morning time so at this time most of the flights would be landing.

Each international airport might have around 5-6 landing runways (assumption) and considering windspeeds(assuming good in all runways at this moment) we might be using all 6. Each 2 mins a flight will be landing (assumption) so while 6 flights (1 batch) are landing another 5 batch might be waiting to land in next 10 mins and will be in air currently. so approx 40 flights.

Total flights in air waiting to land or landing= 40*150=6000

Domestic Airport:

Domestic airports primarily operates during morning hours so most flights will be taking off and landing as well.

Considering 3 runways for landing and 3 for take-off and all working fine in a given windspeed and running at peak capacity we might have 1 batch of take-off happening and another batch of landing happening (1 batch=3 flights) and there will be 5 batches each for take off and landing waiting for their turn in next 10 mins. Since we are focused on flights in air so will consider additional batches only for landing flights.

Total flights in air waiting to land or landing= (3 (Took off) + 3 (Landing) + 3*5( in air waiting for landing)) * Number of airports=20*500=10,000

There might be total of 16000 flights in air at this point in US.

RS. · Answer 9 · 2020-06-04T09:13:58+0000

clarifications:

- does it include international flights while they are in the US territory? - we can consider that

- is it okay to consider only commercial planes? - yes

Approach

domestic flights

find number of flights flying in the air per sec * avg size * occupancy

international flights

same as domestic but calculation of in air will consider only US territory.

Domestic flights

to get number of flights in air, consider number of runways. A big airport might have 25 or so runways while smaller ones will have 1-2. So let's assume avg of 10 runways. a flight typically takes of in like 3 mins from a runway (in a busy airport) and around every 30 mins from smaller ones. So, avg. of around a flight every 10 mins. not considerin the time the spend aligning prior to the runway. so, in a given airport, we have 10 * 60/10 = 60 flights per hour per airport.

a flight takes around 5 hrs from LA to NY and around 45 mins for short trips. So, an avg flight will last for 2-3 hrs. So let's take 3 hrs.

so, in 3 hrs, number of flights in the air are 60*3 = 180 flights per hr per airport.

# of airports: in CA, we have around 2 v.large airports + 10 big airports + 8 small airports = 20 airports. But CA is not an average state. it is on the higher side. So, an avg state should have around a dozen airports. so, total airports in the US = 50*12 = 600

# of domestic flights in air in 3 hrs = 180*600 = 108K , i.e. 36K per hr, i.e 36,000/60/60 = 10 per sec.

this number is much lower than what i expected. I expected this number to be at least 1000 based on the real-time flightaware maps I have been.

the assumption i have made

avg # of runways = 10
avg. # mins between flights takeoff = 10
avg. # hrs in a flight = 3
total # of airports in the US = 600

i believe in a really busy airport, the flights take off maybe every min (i remember once i was #25 in the line for take off and I took off in 35 mins). so, if i change avg. time between flights from 10 to 5, then also my number goes only to 20.

i realized that I had divided the # of flights took off into the air in 3 hrs by numbers to get per sec. But that is wrong because they all will be in air. So,at the end of the 3hr window, in the very second, they all will be in air. i.e 108K planes.= ~100K planes

Continuing the approach, flights have varied occupany and sizes. a typical domestic flight falls into two categories - 200 seater - majority, or a small plane with like 100 seats (maybe like 20%). THere are also super small ones that we could ignore for now.

so, in a given second, there are 80K big planes and 20K small ones, ie. 80K*200+100*20K=18M seats.

so, with an avg occupancy of 50%, we have 9M passengers in air.

International flight

international flights take off from only v. big airports, i.e. 10% of airports = 60.

they typically go west from west coast, east from east coast and the central flights go mostly from the east. so an average timespan of a plane in the US territory (land + ocean) = 2hrs.

flight sizes are big and have higher occupancy rates. So, if they are 400 seats with 75% occupancy, we have 300 passengers per flight. with the same frequency of takeoff, we

#flights per hr per airport = 20 (# of runways assumed)* 6 (every 10 mins) = 120

#flights per 2 hr = 240

from 60 airports = 20400 = ~20K

passengers in the international flights = 20K*300= 6M

so total passengers = 9+6 = 15M

praveeny2k · Answer 10 · 2019-02-12T14:32:27+0000

Assumption 1: Only passenger planes are in the air. (Its not a war time). And, ignoring personal, jet planes, helicopters.

Use cases: Domestic planes, International planes.

Case 1: Domestic planes: Assuming 50*50*2 terminals (50 states, 50 cities in each state, 2 domestic terminals on each airport).

Assumption 2: Assuming it takes 2 hours on an average to reach from 1 city to another in USA.

So, all the planes taking off from a terminal in last 2 hours will be in air.

Assumption 3: There are 2 runways on each terminal and it takes 10 mins to take off a plane.

So, on an average there will be 6*2*2 planes taking off in last 2 hours.

Assumption 4: Each plane carries 200 people.

So, the number of people in domestic planes in the last 2 hours: 200 (people)*24 (planes)*50*50*2(terminals).

Assumption 5: All the airports are operating at their full capacity. And, capacity of domestic and international airport is the same.

Hence, the number of people in the air is : p = 3*200 (people)*24 (planes)*50*50*2(terminals).

Here, 3 signifies for 1 domestic planes, 1 international planes flying inwards USA and 1 international planes flying outwards.

Here, if we assume that the airports are operating at x% capacity so the number will be p*x/100.

where, p is the total number of people calculated above.

Airport	# of Airports	# Runways on Average / Airport	Total Runways
Major	10	4	10 * 4 = 40
Medium	20	2	20 * 2 = 40
Small	100	1	100 * 1 = 100