# Estimation - Number of Airplanes in Air

### Product Management Interview: Guess Estimate the total number of Airplanes in Air

Before jumping in,

**Important Read:**

Now, let go through the solution,

#### Step 1: Clarify the scope of the question

Are we referring to the whole world or are we referring to any particular country like the US?

*A) You can consider the US for this question.*There is a huge variation between the number of airplanes depending on the time of the day (e.g. 2 PM or 3 AM), is it okay to estimate the number for a peak time such as 3 p.m or 6 p.m in the evening?

*A) Yes*Are we talking about all types of planes? like Private planes, Commercial passenger planes, military planes, and Cargo planes?

*A) It’s up to you.*

It makes sense to say that, you'd like to focus on commercial passenger planes for now since they represent most of the airplanes in the air and it narrows down the scope of the question for you further.

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#### Step 2: Create the Main Equation

The key insight to keep in mind is that,

The number of airplanes at any point in time = The number of airplanes that have taken off at some point in the past and have not landed yet.

Let’s say, the average time of a flight for a domestic flight is two hours and for international is five hours. Since the average amount of time is different for domestic and international flights, we would break down the equation into two parts so your main equation would be,

**Total number of flights in the air = Total number of domestic flies in the air + Total number of international flights in the air**

#### Step 3: Break down the unknowns in the equation into simpler equations

Total number of domestic flights in the US air = Total number of airplanes that have taken off from airports of all sizes (small, medium, large, mega).

Total number of departures from each airport size,

= Total number of domestic departures from one airport in that size group **X** Number of airports in that size group

Total number of departures in last 2 hours in one airport,

= Total number of lanes X Total number of airplanes departed per lane per hour X 2 hours

**Total number of domestic flights in the US air,**

= 400 + 1000 + 400 + 5000

= 6800 (approx)

Assumption: Let’ assume an international flight spends 1/3rd of its time in the US air.

**Total number of international flights in the US air,**

= (250 + 1000 ) / 3

= 416 (approx)

#### Step 4: Calculate the Numbers

**Total number of flights in the air,**

**= Total number of domestic flies in the air + Total number of international flights in the air**

= 6800 + 416

= 7200 (approx)

#### Step 5: Sanity Check

Let’s do a sanity check to see if the 7200 flights in the air number we came up with make sense,

Assuming, there are 80 people per plane,

= 80 X 7200 flights

~ 576,000 people in the US air right now.

If we calculate it for the entire day,

**= 576K** per 2 hour x **8** slots of 2 hours

= 4.6 Million (approx)

Multiplying **4.6 M** by 80% to account for less busy times and lower capacity.

The total number of people flying per day in the US,

= 4.6 Million X 80%

= 3.7 million (Which is 1% of the total US population)

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To help you with your Product Manager interview preparations, we have compiled a complete list of the most asked **Product Management Interview** **Questions** and **Answers at companies like Facebook, Google, Amazon, Microsoft, Netflix, etc. answered by PMs at FAANG.**

Now get, **Full Access to All PM Interview Questions and Detailed Answers by FAANG PMs for a Year! Get the Yearly Subscription now!** 👇

**Limited Period Offer**** -** Get Flat **50% discount** on our Yearly subscription! 🙌

**Alternate Payment Methods:**

**Google Pay / PhonePe****Rs.2499**to UPI Id -**mypminterview@oksbi****Paypal****$38**to**mypminterview@gmail.com**

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