The spinner on a Diamond DA40, like on any propeller-driven aircraft, is more than just an aesthetic cover. It streamlines airflow over the propeller hub and, critically, protects the propeller hub and pitch change mechanism from foreign object damage. Integral to the spinner’s structural integrity is the spinner backplate, which forms the aft portion of the spinner assembly and bolts directly to the propeller hub or propeller extension. For DA40 owners in California, Arizona, and Nevada, meticulous inspections and timely repairs of the spinner backplate are paramount for preventing potentially dangerous propeller and engine issues.
At The Aero Center, we are keenly aware of the critical role every component plays in aircraft safety, including the often-overlooked spinner backplate. Our 24/7 maintenance center ensures that these vital inspections and any necessary repairs are performed with the precision and attention to detail that your DA40 deserves, significantly minimizing your aircraft’s downtime. The principle of Consistency guides our comprehensive pre-purchase inspections and routine maintenance, ensuring a predictable and safe operational experience for your DA40.
THE CRITICAL ROLE OF THE SPINNER BACKPLATE
The spinner backplate serves several vital functions:
- Structural Support: It forms the primary structural attachment point for the rest of the spinner shell, which is typically made of composite material on the DA40.
- Vibration Dampening: A properly installed and undamaged backplate helps to manage and distribute propeller vibrations, preventing them from being unduly transferred to the propeller hub or engine.
- Containment: In the event of a blade separation or other propeller anomaly, a robust backplate can offer some degree of containment, limiting damage to the engine or airframe.
- Debris Protection: It shields the sensitive propeller hub, propeller bolts, and pitch change mechanism (for constant-speed propellers) from dirt, dust, water, and foreign object debris ingested during ground operations or flight.
Given its constant exposure to propeller wash, engine vibrations, and potential impacts, the spinner backplate is a high-stress component.
COMMON SPINNER BACKPLATE ISSUES AND INSPECTION POINTS
Spinner backplates on DA40s are typically made of metal (often aluminum) or composite material. Both materials can experience wear and damage:
- Cracks:
- Location: Most common around the mounting bolt holes where the backplate attaches to the propeller hub or extension, and around the cutouts for the propeller blades. Cracks can also radiate from the center hub area.
- Cause: Fatigue from vibration, over-torquing of bolts, stress concentrations, or impacts.
- Detection: Look for hairline cracks in the paint or metal, especially after cleaning. Using a flashlight and magnifying glass, carefully inspect the entire surface, paying extra attention to curved areas and corners. Dye penetrant inspection (a NDT method) can reveal cracks invisible to the naked eye.
- Deformation/Distortion:
- Location: The entire backplate may appear warped, bent, or distorted. The bolt holes might be elongated or “egged out.”
- Cause: Overtightening of mounting bolts, prop strike (even a minor one), impact with foreign objects, or improper removal/installation procedures.
- Detection: Visual inspection from multiple angles. Check for proper fit of the spinner cone onto the backplate. If bolt holes are elongated, the spinner may wobble or not seat properly.
- Corrosion:
- Location: Common on metal backplates, especially in areas where moisture can collect or near dissimilar metal fasteners.
- Cause: Exposure to moisture, prop wash, or fuel/oil residue.
- Detection: Look for white powdery (aluminum) or reddish-brown (steel) corrosion. Pitting can also indicate corrosion.
- Fretting:
- Location: Often seen around the mounting bolt holes where the backplate meets the propeller hub/extension.
- Cause: Microscopic relative movement (slippage) between the backplate and the mating surface, often due to insufficient torque or poor fit.
- Detection: Appears as dark streaks or powdery residue around fastener holes, indicating wear.
- Loose or Missing Fasteners:
- Location: Bolts that attach the backplate to the propeller hub or extension.
- Cause: Improper torque during installation, lack of safety wire (if applicable), or severe vibration.
- Detection: Visual inspection. The spinner may appear to wobble or be off-center during engine run-up.
- Wear from Propeller Blades:
- Location: Along the edges of the cutouts where the propeller blades pass through the backplate.
- Cause: Improper blade tracking, blade bending, or excessive play in the propeller hub allows the blades to rub against the backplate.
- Detection: Look for polished areas, scoring, or material removal on the backplate where it meets the blades. This also indicates a more severe propeller or engine mount issue that needs immediate attention.
Inspection Frequency: Spinner backplate inspections are typically required during propeller removal for overhaul or recurrent inspection, during annual inspections, and after any event that might involve propeller impact (even a minor one, like striking a bird or taxiing over a small object)¹. Diamond’s maintenance schedule (e.g., in the DA40 Maintenance Manual) will specify detailed inspection criteria.
SPINNER BACKPLATE REPAIRS
Repairing a spinner backplate is a critical structural task that must be performed by a certified A&P mechanic, adhering strictly to the Diamond Aircraft Structural Repair Manual (SRM) or FAA-approved data.
- Cracks:
- Minor Cracks: Depending on location and length, some minor cracks might be repairable by stop-drilling the crack ends and installing a doubler plate (patch) using rivets or adhesive bonding. This method is highly specific and must be approved by the SRM.
- Major Cracks/Multiple Cracks: Often necessitates replacement of the entire backplate. Repairing extensively cracked areas is rarely an approved or safe option due to the high stress environment.
- Composite Backplates: Cracks in composite backplates usually require a composite patch repair, involving removal of damaged material, layup of new plies, and curing, all per the SRM².
- Deformation/Distortion:
- Minor Distortion: In some cases, very minor distortion might be acceptable or can be carefully flattened, but this is rare for structural components.
- Significant Deformation: The backplate must be replaced. Attempting to straighten a significantly distorted backplate can introduce internal stresses and cracks, compromising its integrity. Elongated bolt holes also necessitate replacement.
- Corrosion/Fretting:
- Minor Corrosion: Can be removed by mechanical means (e.g., light sanding, abrasive pads) if within limits, followed by proper corrosion treatment (e.g., Alodine, primer, paint).
- Severe Corrosion/Pitting: If the material thickness is significantly reduced or pitting is extensive, the backplate must be replaced. Fretting damage around bolt holes often leads to crack development and generally warrants replacement.
- Loose/Missing Fasteners:
- Repair: Replace missing fasteners with new, approved hardware. Ensure correct type (e.g., AN bolts, self-locking nuts or castellated nuts with cotter pins) and torque to the values specified in the Diamond Maintenance Manual. Use thread lubricant or anti-seize as specified.
- Investigation: Investigate why they became loose (e.g., improper torque, excessive vibration from an unbalanced prop) and address the root cause.
- Propeller Blade Rubs:
- Investigation: Any signs of blade rubbing on the backplate indicate a serious problem with the propeller balance, pitch change mechanism, or engine mounts. The root cause must be identified and rectified first, before any backplate repair or replacement.
- Backplate Repair: The backplate damage itself is then addressed as per crack/deformation guidelines.
Key Considerations for Repairs:
- Approved Data: All repairs must be performed using approved data, primarily the Diamond DA40 Structural Repair Manual (SRM). Deviations require FAA Field Approval or an STC.
- Balancing: After any work involving the propeller, spinner, or backplate, the propeller assembly (including the spinner) must be dynamically balanced to minimize vibration and reduce stress on the engine and airframe.
- Documentation: All structural repairs to the spinner backplate are considered major repairs and require completion of an FAA Form 337³, in addition to a detailed logbook entry. The documentation must clearly describe the damage, the repair performed, and the approved data used.
For DA40 owners in California, Arizona, and Nevada, a vigilant approach to spinner backplate inspections is a small investment that yields huge returns in safety. Early detection of issues can prevent more costly repairs or, more importantly, prevent an in-flight emergency.
The Aero Center offers specialized inspections and repairs for composite aircraft like the Diamond DA40. Our 24/7 service and experienced technicians ensure your aircraft’s spinner backplate is meticulously maintained, minimizing your aircraft’s downtime and providing peace of mind.
The Aero Center is located at William J. Fox Airfield KWJF | Lancaster, CA. Contact us at 209.885.6950 for questions or appointments.
Footnotes:
- Diamond Aircraft Industries GmbH. DA40 Series Airplane Maintenance Manual.
- FAA. Advisory Circular AC 43.13-1B, Acceptable Methods, Techniques, and Practices – Aircraft Inspection and Repair. (Provides general guidance on composite repairs, but manufacturer’s SRM is primary).
- Federal Aviation Administration (FAA). FAA Form 337 – Major Repair and Alteration.
- Diamond Pilots Association. “Cracked Spinner Back Plate.” https://www.diamondaviators.com/forum/viewtopic.php?t=1534