Improving Direct Operating Cost (DOC) help please
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ABF was flying rehabbed DC-9s in such a operation and had an instrument failure at an outstation. They had to hire a LearJet to deliver a replacement. This was the incentive for them to investigate retrofitting DC-9s with glass cockpit - lower DOC plus reliability.
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Given the nature of the ABF operation - hub & spoke, daily pkg sorting window, timing is everything - reliability was a major issue. I am not sure if the glass cockpit would drop into the beancounters' DOC bin, but it was apparently a big issue for them. 
To be honest, I do not know if it was finally adopted; I only know that they had one glass bird (20 yrs ago) flying with an Experimental tag. Even if it were an increased DOC, if it provided greater earnings (lower refund & reputation losses), it might have been seen as an worthwhile upgrade.
To be honest, I do not know if it was finally adopted; I only know that they had one glass bird (20 yrs ago) flying with an Experimental tag. Even if it were an increased DOC, if it provided greater earnings (lower refund & reputation losses), it might have been seen as an worthwhile upgrade.
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Still haven't read the reason, the impetus for changing out the 'system'.
I saw a flight department close because the chief pilot took months to change a GNS XL to a UNS1. He said the GNS was 'dangerous'.
Long before glass and GPS units, planes still went from Point A to B. Big surprise huh?
This thread lives and dies in the world of people wanting new toys in the cockpit and having such a lack of situational awareness that the only way they can fly comfortably is by following a little white airplane on a screen.
I saw a flight department close because the chief pilot took months to change a GNS XL to a UNS1. He said the GNS was 'dangerous'.
Long before glass and GPS units, planes still went from Point A to B. Big surprise huh?
This thread lives and dies in the world of people wanting new toys in the cockpit and having such a lack of situational awareness that the only way they can fly comfortably is by following a little white airplane on a screen.
I need to improve the DOC of the Fokker F27 specifically in terms of the avionics and control system (if applicable). Searching google for an exact definition of aircraft DOC is proving a bit difficult as most sites just give some formula to calculate it but don't really mention anything specifically in terms of time-scales involved.
A good start might be to establish, for typical F-27 operators, what proportion of DOCs is actually represented by maintenance. That will then give you a better idea of the maximum savings that maintainability improvements would produce, which you can then compare with the cost of any such changes.
Bear,
WRT the laptop, simply make it an installed class 2 EFB and that should cover the "Modification" criteria. It could also cover a lot of the functions of an FMC at a much lower cost.
WRT the laptop, simply make it an installed class 2 EFB and that should cover the "Modification" criteria. It could also cover a lot of the functions of an FMC at a much lower cost.
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You mentioned mods cannot be too expensive. Right at the beginning of your assignment it will be necessary to define the chosen F27 model and the limitations of your studies, as it does not sound like this has been done for you. If all those working on the project could agree on a common philosophy, it would be a tiny bit more like the real world where there would be an overall project manager for such considerations.
You might just need to show innovative thought, not just a rehash of what some VIP operator did to one aircraft 20 years ago.
F27 had water injection available for take-off. This provided a respectable amount of extra power for more difficult conditions or for high weight take-off. If these conditions did not exist, water injection is not needed, meaning there was less power and quite a bit less wear on the engine. Reduced wear is a DOC advantage. That is an existing procedure, but could be further refined by "reduced thrust take-off", common on modern jets.
Using a Dry Take-off with further reduction in power would further reduce engine wear. A laptop (avionics) program for each planned airfield could provide the further refined take-off power settings. You would need to co-operate with those who are responsible for engines. Maybe such co-operation is an intended feature of your studies?
Improved navigation would be relatively inexpensive. Even the type of GPS fitted to light aircraft would be usefull. One navigation advantage is more direct tracking can be authorised by ATC with this equipment. A less obvious advantage is that fast and accurate recording of head and tailwinds can help in selection of efficient flight levels. Lower cruising levels are less efficient, but if there is a tailwind at 10000 ft and a 50 knot headwind at 20000 ft, a lower level should be considered to save time and therefore fuel. Again, co-operation with those responsible for operating procedure DOC would be essential.
Some older electronics might be expensive to maintain. Over a few years, a modern full or partial suite of communication and navigation gear might reduce DOC.
I cannot think of any practical thing that could be done with flight controls. Closest would be a modern autopilot. Expensive to fit, but might also be less expensive to maintain. There would be obvious certification problems that might be very costly. Rather than just not mention controls, there would be scope in your studies to list modifications that were considered but rejected.
You might just need to show innovative thought, not just a rehash of what some VIP operator did to one aircraft 20 years ago.
F27 had water injection available for take-off. This provided a respectable amount of extra power for more difficult conditions or for high weight take-off. If these conditions did not exist, water injection is not needed, meaning there was less power and quite a bit less wear on the engine. Reduced wear is a DOC advantage. That is an existing procedure, but could be further refined by "reduced thrust take-off", common on modern jets.
Using a Dry Take-off with further reduction in power would further reduce engine wear. A laptop (avionics) program for each planned airfield could provide the further refined take-off power settings. You would need to co-operate with those who are responsible for engines. Maybe such co-operation is an intended feature of your studies?
Improved navigation would be relatively inexpensive. Even the type of GPS fitted to light aircraft would be usefull. One navigation advantage is more direct tracking can be authorised by ATC with this equipment. A less obvious advantage is that fast and accurate recording of head and tailwinds can help in selection of efficient flight levels. Lower cruising levels are less efficient, but if there is a tailwind at 10000 ft and a 50 knot headwind at 20000 ft, a lower level should be considered to save time and therefore fuel. Again, co-operation with those responsible for operating procedure DOC would be essential.
Some older electronics might be expensive to maintain. Over a few years, a modern full or partial suite of communication and navigation gear might reduce DOC.
I cannot think of any practical thing that could be done with flight controls. Closest would be a modern autopilot. Expensive to fit, but might also be less expensive to maintain. There would be obvious certification problems that might be very costly. Rather than just not mention controls, there would be scope in your studies to list modifications that were considered but rejected.
Last edited by autoflight; 5th Feb 2013 at 02:51.
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Still haven't read the reason, the impetus for changing out the 'system'.
I saw a flight department close because the chief pilot took months to change a GNS XL to a UNS1. He said the GNS was 'dangerous'.
Long before glass and GPS units, planes still went from Point A to B. Big surprise huh?
This thread lives and dies in the world of people wanting new toys in the cockpit and having such a lack of situational awareness that the only way they can fly comfortably is by following a little white airplane on a screen.
I saw a flight department close because the chief pilot took months to change a GNS XL to a UNS1. He said the GNS was 'dangerous'.
Long before glass and GPS units, planes still went from Point A to B. Big surprise huh?
This thread lives and dies in the world of people wanting new toys in the cockpit and having such a lack of situational awareness that the only way they can fly comfortably is by following a little white airplane on a screen.
You appear to be considering operating costs purely in terms of maintenance cost, whereas that only accounts for a proportion of DOCs.
A good start might be to establish, for typical F-27 operators, what proportion of DOCs is actually represented by maintenance. That will then give you a better idea of the maximum savings that maintainability improvements would produce, which you can then compare with the cost of any such changes.
A good start might be to establish, for typical F-27 operators, what proportion of DOCs is actually represented by maintenance. That will then give you a better idea of the maximum savings that maintainability improvements would produce, which you can then compare with the cost of any such changes.
My biggest problem is the "fuel" part of the formula. The calculation for this is extremely complex with variables I simply can not fimd out from the public domain so I have no idea how to apply the formula or if I can just use verbal reasoning with respect to a fuel saving for a system.
WRT the laptop, simply make it an installed class 2 EFB and that should cover the "Modification" criteria. It could also cover a lot of the functions of an FMC at a much lower cost.
You mentioned mods cannot be too expensive. Right at the beginning of your assignment it will be necessary to define the chosen F27 model and the limitations of your studies, as it does not sound like this has been done for you. If all those working on the project could agree on a commom philosophy, it would be a tiny bit more like the real world where there would be an overall project manager for such considerations.
You might just need to show innovative thought, not just a rehash of what some VIP operator did to one aircraft 20 years ago.
F27 had water injection available for take-off. This provided a respectable amount of extra power for more difficult conditions or for high weight take-off. If these conditions did not exist, water injection is not needed, meaning there was less power and quite a bit less wear on the engine. Reduced wear is a DOC advantage. That is an existing procedure, but could be further refined by "reduced thrust take-off", common on modern jets.
Using a Dry Take-off with further reduction in power would further reduce engine wear. A laptop (avionics) program for each planned airfield could provide the further refined take-off power settings. You would need to co-operate with those who are responsible for engines. Maybe such co-operation is an intended feature of your studies?
Improved navigation would be relatively inexpensive. Even the type of GPS fitted to light aircraft would be usefull. One navigation advantage is more direct tracking can be authorised by ATC with this equipment. A less obvious advantage is that fast and accurate recording of head and tailwinds can help in selection of efficient flight levels. Lower cruising levels are less efficient, but if there is a tailwind at 10000 ft and a 50 knot headwind at 20000 ft, a lower level should be considered to save time and therefore fuel. Again, co-operation with those responsible for operating procedure DOC would be essential.
Some older electronics might be expensive to maintain. Over a few years, a modern full or partial suite of communication and navigation gear might reduce DOC.
I cannot think of any practical thing that could be done with flight controls. Closest would be a modern autopilot. Expensive to fit, but might also be less expensive to maintain. There would be obvious certification problems that might be very costly. Rather than just not mention controls, there would be scope in your studies to list modifications that were considered but rejected.
Last edited by Bearcat F8F; 4th Feb 2013 at 16:15.
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Blogname: Long before glass and GPS units, planes still went from Point A to B. Big surprise huh?
F8F ... speaking of the a/p, could it be removed altogether to save weight? ... fly happily without a/p
The real problem with old, obsolete avionics such as the systems you find in a F27 is that they will probably not work for very long, if they do work at all in the first place. The avionics in F27s date from the 1950s (and up to the early 1980s for late models), they cannot be repaired and it is [almost] impossible to find spare parts. Reason why you need entirely new, modern day IFR avionics suite (which, incidentally, are also lighter in weight and offer much more functionality, redundancy and safety).
EFBs (and other gizmos such as iPad, etc.) do not replace panel mounted avionic systems, they are merely tools to improve productivity to some degree within large airlines with large number of flight crew members and well established SOPs. Some airlines use them as an approved way (approved case by case) to store and replace paper documents such as instrument approach plates, airport taxiway diagrams, aircraft POH, MEL, company OPS manuals, etc. EFBs are never approved for navigation, they are usually assigned to a flight crew member, not to the aircraft (NB: if you employ a large number of flight crew members, savings can be substantial). They are not essential in your case, with just one aircraft, just a distraction, IMHO.
Not sure if you have looked into the Garmin suites I mentioned in an earlier post, here are some pics of older turboprops after "affordable" avionics upgrade and, an interesting G1000 video. Glass panel, airport taxiway diagrams and more.
Total installed cost less than 200K USD (no A/P included).
Total installed cost slightly more than 300K USD (fully integrated GFC700 A/P included)
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As you work through the problem, one aspect you will confront is this: "Is the problem adequately specific? Are there enough constraints to determine if a given 'solution' is appropriate?" Anticipated service life of the mod(s) is an example, in which case you could calculate a break-even point where the mod has its initial cost covered and begins to pay off.
OTOH the problem can be OVERSPECIFIED - one constraint conflicting with another.
In either case, point this out to the instructor - backed up of course with an example or two.
OTOH the problem can be OVERSPECIFIED - one constraint conflicting with another.
In either case, point this out to the instructor - backed up of course with an example or two.
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avionmc, thanks for the opinion, much appreciate it. WRT to EFBs I honestly think its rude not to include one. In the worst case scenario, an iPad can be considered a Class 2 EFB. Although I'm unsure if an iPad can be loaded with the required software for takeoff thrust calculations etc. Maybe it can? If not, I am keen on finding some affordable EFBs as it sounds like it's a pretty easy way to improve engine wear and tear, fuel burn and reduce weight.
With that said, I do very much appreciate the need for a new instrument panel. That King Air pit looks great, which brings me onto the next point where I'm struggling:
Is there a place online that I could find out some of the costs associated with these bits of equipment? i.e. new GPS, avionics suite, EFBs etc? Ideally I would also need to work out the depreciation cost and maintenance cost of the unit for DOCsys calculations. But even just the starting cost of buying one of these either new or 2nd hand would be great.
P.S. Whats the reason for having 2 (identical?) GPS units like in the King Air cockpit above?
And also, which GPS's support direct routing? All of them?
With that said, I do very much appreciate the need for a new instrument panel. That King Air pit looks great, which brings me onto the next point where I'm struggling:
Is there a place online that I could find out some of the costs associated with these bits of equipment? i.e. new GPS, avionics suite, EFBs etc? Ideally I would also need to work out the depreciation cost and maintenance cost of the unit for DOCsys calculations. But even just the starting cost of buying one of these either new or 2nd hand would be great.
P.S. Whats the reason for having 2 (identical?) GPS units like in the King Air cockpit above?
And also, which GPS's support direct routing? All of them?
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Cost definition
I think I have a much clearer picture now of what I can do depending on the operating environment however I still find the available formulas for DOC calculation quite confusing. I can't find anything simple and straight forward that I we can use to calculate DOC but I guess that's the nature of DOC.
DOC normally consists of four major cost categories ie. crew cost, fuel and oil cost, depreciation cost (including insurance cost) and maintenance cost.
In your case it might be more transparent to apply the LCC(Life Cycle Cost, the total cost incurred by an item along its entire life / life cycle)concept,instead of the standard Cost Benefit Analysis (CBA) methods. the research is focused on aircraft maintenance and engineering, as the main subject !!!
From LCC point of view, all cost categories resulting from aircraft acquisition and exploitation are included in the LCC, only two cost categories are excluded : Ticketing/Sales/Promotion and General Administration cost !!!
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Would something like this dual display pay for itself in a year of operation by saving on maintenance costs associated with the original 1950s avionics of the F27?
Garmin G3X System Dual Display
So this G3X is £6594. Sounds pretty expensive. Is there any cheaper 2nd hand units such as this? The thing I don't know is actually how much it costs to maintain the original avionics of the F27 in the 1st place. Any guesses on that? Pretty impossible to find such figures online.
The DOCsys formula (for aircraft) has 3 major components. Depreciation + Fuel burn + Maintenance.
We were told as part of the assignment that mods have to pay for themselves within a year or so.
Garmin G3X System Dual Display
So this G3X is £6594. Sounds pretty expensive. Is there any cheaper 2nd hand units such as this? The thing I don't know is actually how much it costs to maintain the original avionics of the F27 in the 1st place. Any guesses on that? Pretty impossible to find such figures online.
DOC is per definition operating costs which are directly attributable to the aircraft being operated. The rest are IOC(Indirect Operating Cost), DOC+IOC= TOC (Total Operating Cost)
DOC normally consists of four major cost categories ie. crew cost, fuel and oil cost, depreciation cost (including insurance cost) and maintenance cost.
In your case it might be more transparent to apply the LCC(Life Cycle Cost, the total cost incurred by an item along its entire life / life cycle)concept,instead of the standard Cost Benefit Analysis (CBA) methods. the research is focused on aircraft maintenance and engineering, as the main subject !!!
From LCC point of view, all cost categories resulting from aircraft acquisition and exploitation are included in the LCC, only two cost categories are excluded : Ticketing/Sales/Promotion and General Administration cost !!!
DOC normally consists of four major cost categories ie. crew cost, fuel and oil cost, depreciation cost (including insurance cost) and maintenance cost.
In your case it might be more transparent to apply the LCC(Life Cycle Cost, the total cost incurred by an item along its entire life / life cycle)concept,instead of the standard Cost Benefit Analysis (CBA) methods. the research is focused on aircraft maintenance and engineering, as the main subject !!!
From LCC point of view, all cost categories resulting from aircraft acquisition and exploitation are included in the LCC, only two cost categories are excluded : Ticketing/Sales/Promotion and General Administration cost !!!
We were told as part of the assignment that mods have to pay for themselves within a year or so.
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DOC
The DOCsys formula (for aircraft) has 3 major components. Depreciation + Fuel burn + Maintenance.
In the real world, it looks more like that.........
Method for Calculating Direct Operating Cost
The following is an estimation method known as DOC+I (Direct operating cost plus interest). This method is based on the work of Liebeck and has been applied by Ross
for wide body commercial aircraft. By definition the DOC+I method takes into account the following operating expenditures; flight & cabin crew cost, airframe maintenance, engine maintenance, landing fees, depreciation, interest, and insurance.
Flight Crew & Cabin Crew
The flight deck and cabin crew cost are all based on Block Hours (BH), which is equivalent to the number of trips per multiplied by the average flight time per trip. For
the flight crew there salary is a function of the maximum takeoff weight of the aircraft as
seen in Equation 1. The flight attendants or cabin crew cost is based on an assumed pay rate of 60 dollars per hour.
(# ) (440 0.532*( /1000) gross Flight Crew = BH × of flight crew × + W (Eq. 1) Cabin Crew = BH ×(#of flight crew)×60 (Eq. 2)
Airframe Maintenance
Cost of airframe maintenance is broken down into three parts; labor, materials, and
burden or the cost of taking the aircraft out of operation.
Airframe Maintenance Labor:
Notice that for both the labor and material cost, are based on a historical curve fit developed by Liebeck and are dependent of the number of trips per year, average trip time and the airframe weight.
Landing Fee
The landing fee is based on the operational empty weight of the aircraft and an average of
landing fees in the United States. They may heavily vary in Europe, with possible
additional fees such as NOX emissions or community noise. However this is not captured in this method.
Depreciation, Interest & Insurance
For all of the following methods the total airframe cost must be known, which can be
found using methods found in Raymer. Notice that all of the following equations are
dependent on gross weight that will be found by your sizing code.
Depreciation (1 residual ) Airframe Cost Airframe Spares Airframe Cost Engine Spares Airframe Cost
For the interest calculation it is ok to set the future value of the aircraft to zero since it is difficult to predict this value, especially at the very early stages of preliminary design. Finally, from all of these the total direct operating cost of a commercial transport can be
found:
DOC = Flight Crew + Cabin Crew + Airframe Maintenance + Engine Maintenance +Depreciation + Insurance + Interest
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Bearcat, You seem to be on a steep learning curve here on pprune, so it seems like you came to the right place.
Reading between the lines, I think the details of your set F27 project are a bit thin. For instance, is your F27 a clapped out piece of s*** that has had a hard life in some aviation backwoods, or is it a VIP aircraft with low hours and no expense spared sourcing a collection of unused or expertly overhauled avionics spares that came with the aircraft? Your class colleages would be interested to know if it was fitted with low time engines and props and who completed the last major service and when.
In the absense of such information, you might need to make a formal assumption about the state of the aircraft and spares.
Reading between the lines, I think the details of your set F27 project are a bit thin. For instance, is your F27 a clapped out piece of s*** that has had a hard life in some aviation backwoods, or is it a VIP aircraft with low hours and no expense spared sourcing a collection of unused or expertly overhauled avionics spares that came with the aircraft? Your class colleages would be interested to know if it was fitted with low time engines and props and who completed the last major service and when.
In the absense of such information, you might need to make a formal assumption about the state of the aircraft and spares.
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Stallfail
That is the biggest amount of academic bull**** that I've heard in my 40 years in the industry. Only the Lufthansa Cost Method was as ridiculous.
AIRLINES DON'T HAVE "METHODS" THEY HAVE CASH IN AND CASH OUT.
Bearcat F8F: Concentrate on cash, cash, cash, not formulae. Cash in vs cash out is what matters. Forget classic DOC methods which include depreciation. Depreciation is not a cost. That's just accountant's mumbo-jumbo. Think about what you could take to the bank (or out). If the changes don't pay off in a year or two your airline could be bust.
Stallfail: what the fuk has cabin crew cost got to do with the problem in hand? Bearcat has to concentrate on the changes, not worry about what stays the same. Luckily academics don't run airlines. At least not successful ones.
P.S. Bearcat: JUST CONCENTRATE ON WHICH COSTS CHANGE, BEFORE vs AFTER. DON'T TRY TO LIST ALL DOC ITEMS. ITS POINTLESS.
You've been given a task unrelated to the real world. You have to do it, but remember the tosser's name for future reference!
AIRLINES DON'T HAVE "METHODS" THEY HAVE CASH IN AND CASH OUT.
Bearcat F8F: Concentrate on cash, cash, cash, not formulae. Cash in vs cash out is what matters. Forget classic DOC methods which include depreciation. Depreciation is not a cost. That's just accountant's mumbo-jumbo. Think about what you could take to the bank (or out). If the changes don't pay off in a year or two your airline could be bust.
Stallfail: what the fuk has cabin crew cost got to do with the problem in hand? Bearcat has to concentrate on the changes, not worry about what stays the same. Luckily academics don't run airlines. At least not successful ones.
P.S. Bearcat: JUST CONCENTRATE ON WHICH COSTS CHANGE, BEFORE vs AFTER. DON'T TRY TO LIST ALL DOC ITEMS. ITS POINTLESS.
You've been given a task unrelated to the real world. You have to do it, but remember the tosser's name for future reference!
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toffeez, Yes, completely agree. I am concentrating on the costs involved in the difference between initial purchase cost + maintenance Vs how much it saves. These DOC formulas are driving me mad. We were not given any realistic data to start with so there is no way on Earth any student could get access to all the costs associated with a F27! so yes, I'm doing exactly what you have suggested.
autoflight, Thanks. I would be quite interested in finding out more relevant equipment for the a/c though. What is the cheapest useful GPS taht I can get for example?
And I can not find a good classifieds website to see listings of 2nd hand units so struggling to find out how much these units cost to buy and maintain and install. Any help appreciated.
autoflight, Thanks. I would be quite interested in finding out more relevant equipment for the a/c though. What is the cheapest useful GPS taht I can get for example?
And I can not find a good classifieds website to see listings of 2nd hand units so struggling to find out how much these units cost to buy and maintain and install. Any help appreciated.
Last edited by Bearcat F8F; 6th Feb 2013 at 09:47.
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Aircraft modification such as flight control and engine retrofits etc unless they are an existing mod are going to cost too much to consider for any normal size operator. So other than removing anything you don't need, to save weight, there is little you can do on this front.
Avionics mods can save you three thing: maintenance costs, weight, and time (direct tracking and lower minimas so less holding or diversions). The equipment in an original F27 will be pretty old and hard to maintain and weighs lots. Wholesale replacement of avionics is expensive but if you can't maintain it the opportunity costs from missed flights could cover the high cost. If the aircraft has supportable avionics keep what you can and go simple. Integration costs can be very high so adding a stand alone GPS will be better value than trying to fit a fully integrated solution. .
Best bang for buck is likely to be dual TSO C145 or 146 GPS and remove the ADF(s). 145/146 allows you to use the GPS as your only destination nav aid which means you can get into more places more often. The ADF then becomes superfluous. Removing it saves you maintenance costs and weight.
Avionics mods can save you three thing: maintenance costs, weight, and time (direct tracking and lower minimas so less holding or diversions). The equipment in an original F27 will be pretty old and hard to maintain and weighs lots. Wholesale replacement of avionics is expensive but if you can't maintain it the opportunity costs from missed flights could cover the high cost. If the aircraft has supportable avionics keep what you can and go simple. Integration costs can be very high so adding a stand alone GPS will be better value than trying to fit a fully integrated solution. .
Best bang for buck is likely to be dual TSO C145 or 146 GPS and remove the ADF(s). 145/146 allows you to use the GPS as your only destination nav aid which means you can get into more places more often. The ADF then becomes superfluous. Removing it saves you maintenance costs and weight.
Last edited by Roger Greendeck; 6th Feb 2013 at 10:25.
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Not sure when your assignment is due but if its after Avalon and you can get yourself along to a trade day there will be lots of component companies there who can give you rough order of magnitude costs.
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Avalon in the UK? Afraid its a bit far for me to go just for a university project. Thanks for the suggestion though.
Is there no good websites where they sell used 2nd hand avionics? All the websites that I come across are limited in the amount of equipment they sell or they don't have a price tag online.
Is there no good websites where they sell used 2nd hand avionics? All the websites that I come across are limited in the amount of equipment they sell or they don't have a price tag online.
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Aircraft modification such as flight control and engine retrofits etc unless they are an existing mod are going to cost too much to consider for any normal size operator. So other than removing anything you don't need, to save weight, there is little you can do on this front.
Avionics mods can save you three thing: maintenance costs, weight, and time (direct tracking and lower minimas so less holding or diversions). The equipment in an original F27 will be pretty old and hard to maintain and weighs lots. Wholesale replacement of avionics is expensive but if you can't maintain it the opportunity costs from missed flights could cover the high cost. If the aircraft has supportable avionics keep what you can and go simple. Integration costs can be very high so adding a stand alone GPS will be better value than trying to fit a fully integrated solution. .
Best bang for buck is likely to be dual TSO C145 or 146 GPS and remove the ADF(s). 145/146 allows you to use the GPS as your only destination nav aid which means you can get into more places more often. The ADF then becomes superfluous. Removing it saves you maintenance costs and weight.
Avionics mods can save you three thing: maintenance costs, weight, and time (direct tracking and lower minimas so less holding or diversions). The equipment in an original F27 will be pretty old and hard to maintain and weighs lots. Wholesale replacement of avionics is expensive but if you can't maintain it the opportunity costs from missed flights could cover the high cost. If the aircraft has supportable avionics keep what you can and go simple. Integration costs can be very high so adding a stand alone GPS will be better value than trying to fit a fully integrated solution. .
Best bang for buck is likely to be dual TSO C145 or 146 GPS and remove the ADF(s). 145/146 allows you to use the GPS as your only destination nav aid which means you can get into more places more often. The ADF then becomes superfluous. Removing it saves you maintenance costs and weight.