Field Approval, Flap Stiffeners for the 170A

[acecabral]

Hello everyone,

I am researching a flap skin repair for my Cessna 170 A and I came across flap stiffeners from McFarlane. I reached out to them for an explanation of why stiffeners were approved for the B, but not the A.

They said, “With this stiffener the issue is mostly legal instead of mechanical. The 170A should have the same airfoil, and therefore trailing edge angle, as the 170B, but the A model did not have a stiffener in the trailing edge and there is no data I could find in the structural repair section of the manual or the parts catalog to support adding one”.

They continue to express that a field approval or a minor alteration would be the next step. So, in an effort to acquire any data on this.

Has anyone submitted a field approval for an A model to install flap stiffeners?

Has anyone had their IA install stiffeners on an A as a minor alteration?

Thank you for your knowledge and time

Patrick Cabral

[voorheesh]

The McFarlane flap stiffeners are for Cessnas equipped with slotted (semi Fowler) flaps. These are a different design from the hinged flaps on the 170A. Would they fit? If so, I would think an IA could advise if they could be field approved. It’s a secondary flight control so I doubt it qualifies for a minor alteration, but that’s a question for an IA or FAA.

Are you dealing with dents (hangar rash) or do the trailing edges need straightening? I used to have a 170A that had some very minor deforming towards the rear of the flaps due to snow. It was not considered structural. We were able to straighten the bends out manually. Ailerons had similar distress we were also able to correct. Both lasted for years with no problems and were never questioned on annuals. There are probably some shops that would re-skin these flaps if necessary.

[acecabral]

Thank you for your insight.

I am dealing with cracks that have circumnavigated around the rivets on the inboard hinges of both flaps. So, I am working on getting my metal prepped for repaint next year. The shop can repair the dents but reskinning controls is bit out of their wheel house.

I am still in research mode, so any data I can gather before going to the FAA would help this side project to fix what is broken and add strength for the future. Aviation is always pushing to learn and make things better, so why not make it better.

Patrick

[GAHorn]

I don’t completely “buy” the McFarlane response, but it doesn’t matter what I think about it since it’s Their Product…They get to say what it’s for.

If it were me I would not install their flap trailing edge stiffener on an A-model, I’d install the Cessna or the generic part instead because it’s thinner as is the A model flap (as compared to the B model). I’d also enter it as a “minor alteration”. It’s a stiffener…not a change of airfoil or function…no different than a doubler or stiffener placed elsewhere. As for a “flight control”…it’s not a balanced control so not adversely affected by the addition. One of the more prominent A models in our fleet has this minor alteration.

Aircraft Spruce sell the same or similar product and (rightly or wrongly) states it’s applicable to “All” models 170. https://www.aircraftspruce.com/pages/me ... flapte.php

But the cracking around your hinges should be addressed with the guidance of 43.13 and the Cessna Structural Repair manuals before anything else is done to the flaps, IMO.

[voorheesh]

Thank you for your insight.

I am dealing with cracks that have circumnavigated around the rivets on the inboard hinges of both flaps. So, I am working on getting my metal prepped for repaint next year. The shop can repair the dents but reskinning controls is bit out of their wheel house.

I am still in research mode, so any data I can gather before going to the FAA would help this side project to fix what is broken and add strength for the future. Aviation is always pushing to learn and make things better, so why not make it better.

Patrick

Regarding “going to the FAA”, I used to be employed by the FAA, not as an airworthiness inspector, but for a time in a supervisory role, so I have some experience in how these inquiries are handled.

If you have experience and expertise to perform repairs, as you describe, then I hope you are able to come up with a good solution. If the repair involves approved parts, guidance from appropriate manuals, or 43-13, there is no reason to involve the FAA, however accomplishment should be by or under supervision of a rated mechanic. The same goes for whether or not to determine minor versus major alterations. The decision rests with the person who signs the maintenance entry. (And subject to FAA oversight and concurrence)

If you lack or may lack experience or expertise, I would be getting a mechanic with IA (preferably the one who will perform subsequent annuals) to be involved in evaluating and helping you get this problem resolved. It needs in person attention IMO. This person will decide when and how to involve the FAA, if necessary.

The only reason I can see requiring contact with the FAA would be for a field approval, if that becomes necessary such as for a repair that is not substantiated by prior FAA approval (approved data). Different FSDOs have different approaches to handling field approvals. Different inspectors may be more (or less) willing to consider these applications. It really helps if the person applying knows what they are doing. I’m serious. We saw too many inquiries from people who didn’t even understand what they were asking for. An FAA inspector has serious responsibility when signing that 337 and they need to trust the person or organization who submitted it. Do not underestimate the role of a good IA in this process. Frequently, inspectors know and trust IA’s and those relationships affect the outcome of field approval applications.

Probably the most misguided application I heard of involved a director of maintenance seeking an FAA airworthiness approval from an office in California who tried to base his case on a loosely similar application that had been approved by an office in Pennsylvania resulting in an intra FAA dustup and an application’s lack of success. The applicant was winging it and clearly didn’t understand what he was asking for. In other words, be careful.

Having said the above, organizations such as this association are excellent sources of information and advice particularly in the realm of relating similar experiences and what works/what doesn’t work. So I hope you get more good advice such as George offered. I can tell you that the FAA considers owners clubs a tremendous asset in aviation safety.

Good luck!

[acecabral]

I don’t completely “buy” the McFarlane response, but it doesn’t matter what I think about it since it’s Their Product…They get to say what it’s for.

If it were me I would not install their flap trailing edge stiffener on an A-model, I’d install the Cessna or the generic part instead because it’s thinner as is the A model flap (as compared to the B model). I’d also enter it as a “minor alteration”. It’s a stiffener…not a change of airfoil or function…no different than a doubler or stiffener placed elsewhere. As for a “flight control”…it’s not a balanced control so no adversely affected by the addition. One of the more prominent A models in our fleet has this minor alteration.

Aircraft Spruce sell the same or similar product and (rightly or wrongly) states it’s applicable to “All” models 170. https://www.aircraftspruce.com/pages/me ... flapte.php

But the cracking around your hinges should be addressed with the guidance of 43.13 and the Cessna Structural Repair manuals before anything else is done to the flaps, IMO.

Thank you GAHorn.

I have found the same product and its McFarlane product sold through Aircraft Spruce. So, I reached out for clarification from McFarlane. They said the statement from the table is in error based on their approved model list.

Yes, I plan to address the cracks first, but if reskinning the metal may open the opportunity to add stiffeners, I wanted to research it first. This is before I pull the trigger on the repair.

Do you have contact information of the owner with A that installed the stiffeners? So I can reach out to them.

Thank you again for your insight.

Patrick

[acecabral]

Regarding “going to the FAA”, I used to be employed by the FAA, not as an airworthiness inspector, but for a time in a supervisory role, so I have some experience in how these inquiries are handled.

If you have experience and expertise to perform repairs, as you describe, then I hope you are able to come up with a good solution. If the repair involves approved parts, guidance from appropriate manuals, or 43-13, there is no reason to involve the FAA, however accomplishment should be by or under supervision of a rated mechanic. The same goes for whether or not to determine minor versus major alterations. The decision rests with the person who signs the maintenance entry. (And subject to FAA oversight and concurrence)

If you lack or may lack experience or expertise, I would be getting a mechanic with IA (preferably the one who will perform subsequent annuals) to be involved in evaluating and helping you get this problem resolved. It needs in person attention IMO. This person will decide when and how to involve the FAA, if necessary.

The only reason I can see requiring contact with the FAA would be for a field approval, if that becomes necessary such as for a repair that is not substantiated by prior FAA approval (approved data). Different FSDOs have different approaches to handling field approvals. Different inspectors may be more (or less) willing to consider these applications. It really helps if the person applying knows what they are doing. I’m serious. We saw too many inquiries from people who didn’t even understand what they were asking for. An FAA inspector has serious responsibility when signing that 337 and they need to trust the person or organization who submitted it. Do not underestimate the role of a good IA in this process. Frequently, inspectors know and trust IA’s and those relationships affect the outcome of field approval applications.

Probably the most misguided application I heard of involved a director of maintenance seeking an FAA airworthiness approval from an office in California who tried to base his case on a loosely similar application that had been approved by an office in Pennsylvania resulting in an intra FAA dustup and an application’s lack of success. The applicant was winging it and clearly didn’t understand what he was asking for. In other words, be careful.

Having said the above, organizations such as this association are excellent sources of information and advice particularly in the realm of relating similar experiences and what works/what doesn’t work. So I hope you get more good advice such as George offered. I can tell you that the FAA considers owners clubs a tremendous asset in aviation safety.

Good luck!

Thank you for insight with FAA

I am not an AMT/A&P nor am I an engineer. However, I am mechanically incline, love aviation, and I want to learn more about my airplane. I also an airline pilot, so I have a healthy amount of respect to stay in my lane till training and certification of oneself is complete.

I have asked my IA for his input and he is also in research mode about this topic. However, he is always between annuals as most IAs are these days. Hence, asking the collective mind about this topic.

Thank you, again, for your intel about inner workings of the FAA.

Patrick

[c170b53]

Yikes ! not an airline pilot trying to fix a plane . I spent several hours helping an airline pilot hunt down a short causing a circuit breaker to pop only to find he had replaced a single contact bayonet bulb with a double contact bulb. Stupid, I know I should have found the short in a few minutes
Patience, collecting the information for the task, having the tools, practice, hand eye coordination all help in the quality of the product. I’d say most can come up to speed to work on their plane by finding someone to provide oversight. Those second pair of eyes never hurt, they’re needed for safety and ultimately oversight provides learning assistance.
Good luck with your flaps and your plane.