Best design to deal with subclasses of a database?

I have a class called a Plane.

class Plane {
   private int _planeId;      

   public int getModel() { }

   public int getNumberOfPassengers() {}
}

And I another class called PlaneService which depends on plane and adds some logic to it,

class PlaneService  {
   private Plane _plane;

   public PlaneService(Plane _plane) {
        this._plane = _plane;
   }

   public void validdatePlane(int planeId) {
       fetch plane from planeId from db.
       if ( plane.getNumberOfPassengers() is in range of {100 to 300} )
          plane is valid.
   }
}

But now a new requirement comes in: plane must be extended to support fighter jets. So new design looks like this:

   class Plane {
       private int _planeId;      

       public int getModel() { }
    }

    class PassengerPlane extends Plane {
       public int getNumberOfPassengers() {}
    }

    class FigherJet extends Plane {
      public boolean isCommissioned() {} 
   }

My question is how can I best design 'PlaneSvc'in OOP way ? Is there a good design pattern ?

Currently, my code looks like this:

class PlaneService  {
       private Plane _plane;

       public PlaneService(Plane _plane) {
            this._plane = _plane;
       }

       public void validdatePlane(int planeId) {
           fetch CommercialPlane from planeId from db.
           if (commericialPlaneObject != null) {
              if ( plane.getNumberOfPassengers() is in range of {100 to 300} )
                 plane is valid.
           } 
           fetch FighterPlaneObject from planeId from db.
            if (FighterPlaneObject != null) {
                if (fighterplane.isCommissioned()) {
                   return validPlane;
                } 
            }
       }
    }

I am sure there is some design pattern to deal with such a case. I need to understand a cleaner approach to if-else here.