[author]This write up has been provided by George Merle. He has over 4,000 hours flying experience with most of it in F-18 and F-14 aircraft as a Naval Aviator. He has an ATP and CFII and at the time of this writing flys for Skydive Suffolk in Virginia which was the first US DZ to purchase a PAC 750XL. Thank you George for your service to our country and your contribution to this site.
An addendum provided by Philip Esdaile has been added below. His background is 2600 hrs TT 7000+ landings, Commercial Pilot SEL, A&P IA 40 years, Proposed the P750 project and its minimum performance specs to Pacific Aerospace. Consulted during certification. Importer and Service Center. President Utility Aircraft Corporation.[/author]
The PAC 750XL is a utility aircraft with incredible performance, strength, and capacity. The 750XL was designed specifically for sky diving but can serve a wide range of duties including freight, passenger operations, photography, or agricultural work. For hauling jumpers, nothing’s better. It’s just about the perfect airplane. It has superb short takeoff and landing capabilities and the thick cord / high lift wing make getting to altitude with a heavy load of jumpers a snap. Initial climb rates exceed 2000 ft/min with 700lbs of fuel and 14 jumpers and above 12,000 ft. climb rates will continue to exceed 1000 ft/min.
Here are some of the specs:
- Pratt & Whitney PT6A-34 750hp engine (4,000hr TBO)
- Pilot + 9 passengers or 17 parachutists
- Maximum takeoff Weight 7,500 lbs
- Basic Empty Weight 3300 lbs
- Useful Load 4,200 lbs
- VY 90 kts, Cruise 169 kts
- Typical jump run max fuel load, 850 lbs
- SL to 13500’ and back, fuel burn approx. 100lbs or 14.7 Gal
- Cabin 54 ” wide, 56″ high and 158″ aft of pilot
- 150 hour maintenance cycles
- To 13,500 ft from brake release in under 13 minutes
The PAC 750 XL is a bone simple airplane. It’s an all metal, riveted, stressed skin construction with a single cantilever low wing and tricycle undercarriage (down and welded). All the flight controls are non boosted manually operated cables, push rods and torque tubes. The cockpit accommodates two pilots side-by-side with access via hinged doors on either side of the cockpit. It’s nicely equipped with dual Garmin 430’s and full set of Electronics International (EI) instruments.
The main cabin/cargo area is roomy and jumpers can sit side by side facing aft on bench type seats. The wing is the most striking external feature of the airplane that catches everyone’s eye almost immediately. The wing is basically made up of two sections…outboard and inboard. Throughout the entire span the wing has a constant chord and a constant aerofoil section. The inboard section of the wing has no dihedral and the outboard part of the wing has a dihedral angle of 8º. This combination maximized available lift while maintaining adequate lateral stability. An incidence angle of 2º is maintained throughout the span.
Single slotted flaps are fitted at the trailing edge of the inboard portion of the wing. Conventional ailerons with balance tabs on both ailerons and an electrically operated trim on the left hand aileron are attached to the outer panels. Flaps are exceedingly effective and take off are performed with no flaps and landing typically with ½ flaps.
The stability of the A/C, and its’ low speed performance make it a pretty easy to fly. The CG envelope is “gi-normous” (generous). If the cabin is full then the jumper’s weight is spread out correctly. If there are only a few jumpers they can literally sit anywhere they want with little or no adverse effects to the CG.
The passenger/cargo door is located on the left hand side of the fuselage behind the wing trailing edge. The door is approximately 50” wide and 47” high at the front and 41.3” high at the rear. It slides up into the cabin for ingress or egress and can be opened or closed from both inside and outside.
Take Off and Climb
What surprises you is how fast it’s ready to fly. If you add the power smoothly, by the time you get to the throttle stop or reach a torque or ITT limit you’ve past lift off speed usually around 65-70 kts. (depending on weight and temp). With ½ flaps selected, it has none of the unpleasant tenancies that you might associate with a big single engine aircraft. A little right rudder is all that’s required to keep it tracking straight. If I had to find fault I’d say that the PAC wants to fly “too soon”. The best method for achieving a clean crisp take off is to hold slight forward control pressure keeping the nose wheel on the runway until lift off speed is achieved. Add slight back pressure and it pops off the ground nicely.
Climb out, even with a heavy load is just phenomenal. The big Hartzell prop grabs the air and pulls the aircraft skyward at an amazing rate. Vx is 80 knots and Vy is 90. However I’ve found that holding 91-93 knots typically produces a slightly higher rate of climb. I’m not sure why, but a little faster than book seems to work better on climb out. With typical loads I’ll see 8000 ft in about 4-6 minutes and 12000 in less than 10 minutes. Above 10000 ft climb rates are close to 1000 ft/min so it makes the math easy to reach jump altitude (13,500) in most cases and the “spot” at the same time.
Jump Run
The jump run is also fairly straight forward. Set up the Garmin with the Drop Zone (DZ) coordinates in a user waypoint; select direct to the DZ and use the OBS function to set up the run in line. The GPS shows time, speed, distance and cross track error. All the pilot has to do is make small timing corrections for whatever DME offset the jumpmaster and pilot agree on.
Aircraft configuration is also pretty simple. Arrive at the drop point with about 80-85 knots KIAS, ½ flaps and 30 lbs of torque to hold altitude. When it’s time for the green light to come on, bring the power back to 15 lbs of torque and the prop back to 1880 rpm. Allow the plane to slow then descend to maintain airspeed between 70-80 knots. This configuration and airspeed make the exit comfortable for the jumpers, especially if there are 4-ways that have to hang outside for awhile.
As the jumpers leave there will be a slight forward pitch as the weight in the back suddenly disappears. It’s very controllable with just a slight amount of trim or aft stick pressure. After everyone is out pull the handle above the pilots head to close the door, raise the flaps, turn off the jump lights, go to idle power and prop where it was for the descent.
added by DiverDriver.com: Be aware of jumpers blocking airflow over the elevator. Watch this video:
Descent
Idle power and 1880 on the RPM’s to keep the noise of the prop down. If you run the prop faster you’ll make one heck of a racket on the ground and the locals will probably call to complain. Close the door and descend at 160 KIAS. This configuration will keep you well within the green arc and coming down at a respectable 3000-4000 ft/min.
To keep the boss happy idle descents to touchdown are the goal. It uses less gas and builds dead-stick skills rather quickly. A good rule of thumb for pattern is to be at about 4000 ft on a mid field downwind and 2000 ft for the turn to base. After that I just eyeball the landing using flaps 20 degrees and point the nose 200-300 yards short of the runway threshold. This usually yields about an 85-90 knot approach speed. This is about 30 knots above touchdown speed. That’s why you’ll need to point the nose at the grass short of the runway. Use the round out to the flare to bleed off excess speed and touchdown on the first 500 ft of paved runway. Once you begin to round out the descent and start your flare airspeed decays rapidly. Make sure you’re over pavement with the wheels just a few inches off when the airplane quits flying. Post landing checks are simple. Leave the flaps alone because you’ll need the at 20 degrees for the next take off and reset the trim.
Try to keep fuel levels between 850 lbs max and 250 lbs min. This gives you enough fuel for 6 loads without having to get gas while at the same time keeping the Weight & Balance well inside the envelope.
Philip Esdaile
Addendum to George Merle’s excellent write up.
PAC 750XL (AKA P750 )
As a long time P750 pilot and mechanic, I would like to add some important insights to George Merle’s excellent article. Over the years, I have run up to three stop watches on myself to see where time is gained and lost. This idea, like all good ideas, was stolen from another pilot. It turned out to be an amazing revelation, just like lap times on a race track. As you gain confidence in yourself and the plane, relaxing into it, you can integrate timing into your jump run. Seconds count.
I accomplish the flight with the fuel control in “ground” idle. More on this later.
It is important to utilize the Inertia Separator (IPS) for ALL ground ops. We have seen multiple engines with FOD damage of startling and expensive proportions. Sadly, the log book on one aircraft showed two instances of FOD damage rework by an engine shop, on the same plane. Clearly, this huge cost could have been avoided by strict use of the IPS system. We have noted a lot of debris thrown into the air when the prop is feathered prior to shut-down and the aircraft stationary. This uplifted debris seems to go straight down the intake system, exactly the same way it does on all the other PT6 powered aircraft. It is really simple to see if the pilot is doing his job with the IPS by looking down the intake system at the vane. If the vane is visible and covered in bugs, the IPS isn’t being used. If the vane isn’t visible, it’s behind the door. Switching the IPS to “Normal” will allow the visual inspection. There is no reason the vane should have bugs.
The main landing gear are located quite a bit aft of the center of gravity. This is an awesome feature as the plane will never sit on its tail during loading. Review your weight and balance to see how much weight can be put inside the cargo door. It’s a BIG number. However, on the take-off roll your stick pressure isn’t pitching the ship around the C of G fulcrum, its pitching the ship up and rotating it around the main wheels. Heavy stick pressure is needed. But the good news is, when you have enough aerodynamic elevator pressure to do lift the nose wheel, it’s near impossible to pop a PAC 750 off and into ground effect. You ARE going to fly and climb! Immediately the plane is airborne, the plane is pitching about the center of gravity and the stick pressure is normal. This means that on a short take-off at max gross takeoff weight, neutral stick used until around 50 KIAS, then increase back pressure to lift the nose (will be a heavy pull), then all normal as you break ground. You will see pilots running down the runway with the mains off and the nose-wheel on, as the pilot is waiting for an already flying plane, to fly. The plane is well ahead of the pilot !!!!
Take-off should be accomplished with less than max torque if the runway has the length. I take-off with 60 PSI and the IPS on. This gives me a margin to allow the torque to increase with airspeed with ram air pressure rise with the IPS is selected to normal. . Once above the tree line (the bug zone), switch the IPS to normal and reset the torque to 64 PSI or 740 ITT depending on the temp. 740 ITT is the published “Max Continuous” temp and has served us well to TBO and beyond. Constantly running at max ITT 790 can shorten the hot section life. Running less than 740 ITT reduces climb efficiency with no increased benefit to component lifespan.
Climbing at 64 PSI usually results in a hard climb that puts the engine on its natural decreasing torque curve and 55 psi in around 5 minutes. As George states, around 91 KIAS is a magic number. It’s also the number where the rudder trim stay’s effective. Under 90 and you will have to carry right rudder. Depending on the aircraft and the engine, I have found some aircraft to do slightly better at 100 KIAS. Three props are approved for the PAC750XL. The standard “stump pulling” three blade Hartzell, the four blade Hartzell and the four blade MT. Each have their own characteristics.
Keeping the torque up and the ball centered is extremely important. Those of you who are religious about keeping the ball centered already know this and can out work your counterpart to an astonishing degree. This means ball centered, in all flight conditions, all the time. ALL THE TIME. All aircraft fly better when they are flying straight and not slightly sideways.
I try to limit my turns to 10 degrees of bank angle in the PAC 750XL. This means you need to pay attention to your climb. The aircraft climbs better when the wings are level. This means that I am entering the jump run from 3,000’ in the climb. If I am squared away in this four dimensional puzzle at 3,000 feet, it all comes together like magic at 12,500. Arriving neither too early nor too late. Fly the aircraft very smoothly. A smooth pilot will give himself some street cred, make the plane perform better, use less fuel and be less tiring for the pilot. A win.
Depending on the outside air temp and the engine itself, keep the torque up until 740 ITT. If 740 is un-obtainable, discuss it with your maintenance personnel and reference the PWC manual. You may be somewhere really cool, or you may have a rigging issue. We check the Torque and ITT calibration every second maintenance check. The Electronics International (EI) gauges are very accurate and easily adjusted in the field. We mount the torque transducers with the wires down (per EI) which solved a lot of transducer issues.
The jump run can be full of surprises to the unwary.
Have a look at your W & B as the jumpers exit. Just for fun, assume a 6 way group in the door, and another 6 way in the plane (this isn’t such an issue for tandem only ops). It’s the second 6 way group that has the biggest C of G influence. Just when you were relaxing from the first group, boom! Sometimes, a group will hang on for longer than it should. If you get slow, things can get funny as you run out of nose down trim then nose down stick. The plane will start an uncontrolled pitch up. You don’t want this. The tail is going lower and this 1000 lbs of humans are heading straight for it. We have never had the plane stall or even heard of it stalling. The video above is the elevator getting to the mechanical stop and the aircraft will pitching up. I’m sure someone has gone for the full stall ride but they are not saying.
When you are trimming and applying forward stick, you have no idea where the stick position is with relation to the forward stick stop. However, if the right hand stick is in place you are in luck. On the ground, push the stick to the forward stop and look at the co-pilot stick in relation to the circuit breaker panel. Reach over with your right hand flat. Will two, three fingers fit in this gap? Make a note of this distance. Then when you have this group hanging on, you can look over, gauge the distance and plan your next move. Make a fast decision because it this point things happen really, really, quickly.
If you conclude things are going to go from worse to worser, put the stick full forward, full left and apply full left rudder. This will roll the plane on its side and lift the tail with the now horizontal rudder. The jumpers will be instantly gone. This maneuver can be done so quickly, with a fast recovery you will still be on the jump run with wings level with practically no altitude loss. You must maintain positive control of the aircraft at all times. This technique was taught to me by Ray Ferrell. It worked for him and has served me and everyone we have trained. You should train for this without a load of jumpers. It should be part of the DZ’s training so that when it happens, everyone has a full and complete understanding of what happened and why. The PAC 750XL is a truly docile plane at slow speeds. It has great roll control and light controls. It will do things for you that other aircraft struggle with or bite you for even attempting.
At the end of the jump run descend straight ahead as it will be less stress on the gyros and airframe with no measurable gain in time. The torque will be at zero. You will lose a lot of altitude before the airspeed gets up to 160 KIAS which is the target with the door closed and the flaps up. 160 KIAS will get the PAC 750 from the end of the jump run to wheels on the runway in around 2 minutes. The PAC 750 is amazing as it descends so rapidly. (The four blade Hartzell gives the highest rate of descent). With the high rate of descent from 12,000 feet you cannot stray away from the pattern. The descent sight picture takes some getting used to. This is also where ground idle on the condition lever really works well. While it makes little difference to the descent rate, if you fly around 500 hours a year, you will save an additional $2-3,000 in fuel. The engine burns around 145-165 pph at flight idle and 115 pph in ground idle. Seconds, minutes, hours and fuel all add up.
I maintain 160 KIAS down to around 500 feet agl, start rounding out to the runway and bring the prop lever to max RPM. The round out is simply trimming, being gentle with the control inputs. As the nose comes up, all the parasite drag works and the speed drops away. Depending on the engine rigging, (you may have a nicely rigged machine), somewhere around 110 KIAS, the prop will go flat, all by itself, with no detrimental effect other than the airspeed quickly decreases from 110 to 70 in about three seconds. Around 70, the prop angle changes again by itself and you are about 100 feet above ground (AGL) where the IPS is selected to ”On” prior to entering the bug zone. Sometimes I use 20 degrees of flaps, other times I use none. I like the pitch control with zero flaps, but in the end, the flaps are just another tool to get the landing job done.
When you touchdown, move the power lever through the gate into a range Pratt defines as “Ground Taxi”. This is the range with the prop pitch is zero. It is neither pulling or reversing. To become familiar with “Ground Taxi” simply taxi to a stop on a level surface and move the power lever through the gate and listen. Release the brakes and arrest any forward or aft movement of the aircraft with the power lever. With the brakes off and the aircraft stationary you will hear the sound you want to hear often. Note also the position of the power lever in the quadrant. Between this point and the gate is “Ground Taxi”. It is also known as the “dead band” because nothing is happening. This can be rigged by your maintenance personnel. I prefer a wide dead-band as it’s less tiring than a hair trigger whereby you shoot through the dead-band into reverse. There is no need for reverse. On touchdown, moving the power lever into ground taxi is all that’s required to reduce trust, save the brakes, save the prop and save uplifting dirt to be ingested in the engine. If you start with a freshly painted prop and a little practice, you can see the results of your engine management. Actually, everyone gets to see the results of your engine management. Some pilots have fresh looking paint after 150 hours, and others don’t. The ones that don’t usually have a first stage compressor that looks like the prop leading edge. There is a direct correlation. Don’t be that guy. If you need reverse due to some unforeseen circumstances, go for it. But reverse doesn’t have to be your normal procedure.
Taxi back to the loading area controlling the ships taxi speed with the power lever only. Braking only as required Yup, that’s where you get that cool sound specific to the PT6.
ENGINE FAILURES
Go out with a check pilot and practice. Have the second pilot adjust the power to maintain a 700-800 ft/min descent rate with the prop control full forward. DO NOT PRACTICE BY FEATHERING THE PROP. Bad things can happen. This will simulate a feathered prop with “zero-thrust” setting.
Assess IMMEDIATELY. Is the prop feathering or not? If the prop is feathering, nice. If it’s not, FEATHER IT. Maintain best glide. DON’T panic. This airplane will fly around with a feathered prop for an extraordinary amount of time. You think you know this plane inside and out, but with a feathered prop, you are not flying a jump plane anymore, you are flying a General Aviation Part 23 certified turbine.
Look around if you have time. Look at a few choices and pick one appropriate for the occasion. If you put the jumpers out at 12,000 feet, you may have 10 minutes of descent time. Is the compressor running? It may be idling at 52%-69%. ITT? Remember, the power lever is controlling air which controls the fuel. You may be able to increase the compressor speed with the Emergency Power (EP) control. Do you have options? DO NOT DO A SKYDIVE DESCENT. Manage your descent and look around. Plan your approach speed. Remember your PAC750XL training flights when you saw 35 KIAS stalls when light weight. Think about an approach speed of 1.3 Vso. Wow, an approach at 45? Yup.
Don’t go fast, you have NO PROPELLER BREAKING. If you touchdown too fast you will lock the brakes and still crash at the departure end of the runway. If you are lucky, you won’t hit the trees. More than likely you are being watched with a GoPro. You will have a lot of time to think about what you “shoulda done”. Think about this now.
DON’T RUSH. Remember your student pilot training. It applies here. Dead stick is two events. Event number one is to fly the plane to 1000’ AGL downwind the landing area. Second is to fly the pattern from position number one to the runway. Aim for the middle of the first third of your chosen landing area. This allows for some undershoot without using up too much valuable space. You don’t want to come in fast and end up floating long past your intended landing area. DON’T BE A PASSENGER. This plane will do stuff for you if you make smart choices.
There have been a few dead stick landings in the PAC 750 for various reasons. Some have had great outcomes, others, no so much. One was a power loss and feather at 300 ft agl after departure. Pilot,s choices were trees, a road that terminated in an electrical sub-station, or a 100 degree turn back to a taxiway. The turn was made, trees cleared and a roll-out on the taxiway. The pilot stated the plane was slowing up but so solid and responsive he had complete confidence in the outcome.
Enjoy this awesome plane!