<select> dropdown is not recognizing the property from the ViewModel in view using ASP.Net Cor-CodePudding

I am working on the ASP.NET Core 6 MVC. In view I have created a dropdown with tag. I am trying to bind this dropdown from the ViewModel by following a tutorial from Microsoft document. I think I am doing everything alright but missing to get the result.
When I try to bind the with the property, the property is not recognized. Please see the code below.

//View : See the code for select. The SelectedValue and Model.ddAircraft are not recognized.

@model IEnumerable<Lsap.Models.PlannedPartInstallationViewModel>

<div >
    <label for="colFormLabelSm" >Aircraft</label>
 
    <div >             
       <select asp-for="SelectedValue" asp-items="Model.ddAircrafts"></select> 
                
    </div>
  
</div>
<div >
    <label for="colFormLabelSm" >Disk #</label>
    <div >
        <input type="number"   name="txtDisk" id="txtDisk" placeholder="">
    </div>

</div>


</form>

 <table >
   <thead>
    <tr>
         <th>
             @Html.DisplayNameFor(model => model.DiskNumber)
         </th>
         '<th>
             @Html.DisplayNameFor(model => model.PartID)
         </th>
        
</thead>
<tbody>

@foreach (var item in Model) {
    <tr>
        <td>
            @Html.DisplayFor(modelItem => item.DiskNumber)
        </td>
        <td>
            @Html.DisplayFor(modelItem => item.PartID)
        </td>
        
      
    </tr>

 }
   </tbody>
</table>

//Action Method:

public IActionResult Index()
    {
        var data= _aircraftBu.getAircraft();

        List<SelectListItem> dropdown = new List<SelectListItem>();
        foreach(var a in data)
        {
            var listItem = new SelectListItem();
            listItem.Text = a.Registration;
            listItem.Value = a.Registration;
            dropdown.Add(listItem);
        }
        dropdown.Insert(0, new SelectListItem { Text = "0", Value = "Select Item" });
         var listPPVM = new List<PlannedPartInstallationViewModel>();
        var plannedPartInstallation = new PlannedPartInstallationViewModel()
        {
            ddAircrafts = dropdown,
            DiskNumber = "33342",
            PartID = 12343,
            SelectedValue = "Select Item"
        };
        listPPVM.Add(plannedPartInstallation);          
     
        return View(listPPVM);
}

/ViewModel

   public class PlannedPartInstallationViewModel
{
    
    public int PartID { get; set; }
    public string DiskNumber { get; set; }

    public string SelectedValue { get; set; }
    public List<SelectListItem> ddAircrafts { get; set; }
}

}

And this is the link I followed for Select tag helpers.