In our articles we have already mentioned many times that safety and security of passengers and aircrafts are the most important things. Nowadays, without a key or a password, you can't enter almost anywhere, for example building, apartment, car, bicycle, workplace, ATM, etc. So, the logical conclusion would be that aircrafts demand higher level of security and safety than just usage of keys and passwords, as there is a high risk for human health and potential material damage if misusage appears.
There is no simple answer to this question, so we will try to explain if the key is necessary or not and what kind of additional security measures should be followed by using few airplane models as samples.
A glider is a type of an aircraft that is usually parked inside of a garage or a special transport trailer. Furthermore, they are usually stored inside of objects that have their own locking systems, so in most cases, the pilot can enter the glider just by using a handle that can be reached through a hole installed on the glider's window. In addition, gliders don't have an engine, so there is no need for the key to start the engine.
Civil utility aircraft
As a second example we took Cessna 172 aircraft as one of the most popular aircrafts that is mostly used for educational purposes. Cessna 172 is a single-engine aircraft that had it first flight on 1955. Usually you can see this aircraft both on big airports as well as on smaller airports. In addition, it is often parked on large open spaces where there is a lot of people, so this aircraft type has a safety lock in order to prevent some kind of misusage. The key of Cessna 172 has additional purpose to start the engine, because most of the general aviation aircrafts has electrical engine starter similar to engine starters installed in cars.
Cessna Citation is a good example for business jets. The Cessna Citation family is forming the largest business jet fleet. First flight of Cessna Citation was recorded back in the 1972. Same as for the civil utility aircrafts, these types of aircrafts has keys for door opening and to be able to use aircraft steps to enter the aircraft. Also, this key can be used for cargo departments. But, this key is not used to start the aircraft engine, although some of the business jets have additional safety system for electrical system to be turned on by using keys.
Probably you had most chances to see this type of aircrafts as a passenger. For jet airliners there are special door opening procedures that can vary based on the model of aircrafts as well as on the airline specific rules, but there is no case that you need a key to lock and unlock the doors. Also, you don't need the key to start the engine. But we suggest you to see a couple of videos that will give you a better picture how to operate the aircraft doors and how to start the engine.
Door operation procedure:
Start up procedure:
There is a certain question that can logically pop up after all these explanations, and that is how is it possible that jet airliners doesn't have the keys? The answer is very simple and basically the main reason for this is that all of the aircrafts are parked inside the highly secured areas. Airside area is under the constant CCTV surveillance and under the monitoring of airport security officers. It is important to say that everyone who works at the airside needs to pass the background criminal record check and also once someone enters the airside he needs to pass multiple control points. Furthermore, in some cases aircraft doors are sealed with special numerical stickers that guarantee that no one enter the aircraft.
As you can see, there is no simple answer to our question whether the pilot needs a key or not to open and start the aircraft. We can only come to conclusion that jet airliners don't need key for door opening nor starting the engine, because they are parked at the designated area with the high security level. On the other hand, smaller aircrafts that are often parked in big areas with lower security level usually need key for door opening and some additional safety procedures such as inability to start the engine without a proper key.