If you are new to the Bonanza or an experienced Bonanza owner/pilot

give this secondary cowl safety minor modification narrative some serious consideration with your mechanic.

A Beechcraft Bonanza (Model 35/33/36 series) is known to have Hartwell-style latching mechanisms on its cowl doors, which have been involved in several incidents where they opened in flight. These failures are frequently attributed to improper securing during maintenance or preflight inspections, leading to significant drag, structural damage, or emergency landings.

• Failure Mechanism: The Hartwell latch is designed to be flush, but if not fully engaged and locked, air pressure can cause the cowl door to open.
• Safety Risk: While an open cowl often causes distraction, the primary danger is the potential for the door to tear off or strike the propeller, or for the pilot to stall the aircraft while distracted.
• Recent Incident Analysis: In a 2025 incident, a pilot experienced a cowl blow open but managed a safe landing by focusing on aircraft control, highlighting the importance of not overreacting.
• Previous Incidents: The NTSB has investigated multiple occurrences where cowl latch failures resulted in damage or loss of control.

The above images illustrate the potential in-flight disaster that can befall a Bonanza owner/pilot whose latches are not properly engaged or adjusted properly.

The below picture shows the Hartwell jaws that grab the cowling circular pin that secures the cowl door down. If these jaws and the entire latching mechanism are not adjusted properly, the jaws will spread just enough to allow the circular pin to escape the jaws and then the in-flight mayhem as seen in the above images starts!

My hangar neighbor, V35B Bonanza owner and IA rated mechanic, developed a "minor modification" for his Bonanza that adds a "secondary safety" to the Hartwell Latch equipped Bonanza engine cowls.

It's actually simple as well as elegant and consists of the following items on each cowling side:

• 10-32 x 1/2" Pan Head Machine Screw
• 10-32 Nut Plate MS21069L3
  
• Size 10 Plastic Washer

Below are the pictures of his minor modification which only requires a few extra seconds during pre-flight to remove the screw for engine bay and oil level inspection. Click the image for a full size image in another browser window.

In my IA's view this is a "minor modification", but like doctors, lawyers and accountants, there may be differences of opinions. YOUR mechanic/IA is the final arbiter of any certified aircraft modification, so consult yours accordingly before deploying this modification!