HS-125-1A
Luxury Jet of the Flintstones

Limitations
Max Ramp Weight
21,400 lbs
Max Taxi Weight 
21,400 lbs
Max Takeoff Weight
21,200 lbs 
Max Landing Weight
19,950 lbs 
Max Zero Fuel Weight
13,200 lbs 
Max Alt T.O. & LDG
 9,000 ft
Max Enroute Altitude
41,000 ft
Min Temp T.O. & LDG
-40 Deg C
Max Temperature
ISA + 30 C
Max Tailwind T.O/ LDG
10 kts
Max Runway Slope
2%
Max Fuel Imbalance
500 lbs

Speeds
Vmo/Mmo
290 kts / .735 Mach
Va
180 kts
Vle / Vlo
210 kts
Vsb
No Speedbrakes with Flaps extended when airborne.
 Vturb
210 kts / .63 Mach
Vfe
Flap  10  Deg  210 kts
25 Deg  160 kts
50 Deg  145 kts
Load Factor
Flaps Up      2.9 G
Flaps Ext     2.0 G
Max Engine Overspeed
103% for 20 sec
Max Engine RPM / EGT
100% / 695 Deg C
Min Oil Temp for Start
-40 Deg C
Min Oil Press @ 95% RPM
27 PSI
Max Oil Consumption
1.25 Pints /hr
Max Occupants
11 persons

Minimum Brake Cooling Time
Flap 15 Takeoff
  5 Minutes
Flap  0 Takeoff 
10 Minutes
After Abort
25 Minutes
After 2 Aborts
45 Minutes

Note:   If Takeoff Weight is to exceed 20,500 lbs, consult the brake cooling chart section 4 page 19 of the AFM.
 
 
Autopilot Limitations

 Do not use auto pilot below 200 kts Flaps Up as per section 2 page 15 of the AFM.   Auto pilot altitude hold must remain disengaged during severe turbulence. No auto pilot use above 15,000 ft at speeds less than 155 kts or less than Vref + 20 kts below 15,000 ft.   Auto pilot must not be used below 1,300 ft except on a coupled ILS approach.  Coupled approach be flown to 240 ft AGL.  When auto pilot is in use, aft CG limit is 1% MAC forward of normal limit.
 
 
Engine

    The Rolls Royce Viper engine powers all of the "Straight Pipe" Hawker Jets.  It was originally designed to power drones, and be destroyed by some new weapon system in short order.  It did, however, turn out to be a very reliable engine, and was installed on the Hawker Jet.  One odd thing is that there was no provision to recover the oil that is used to lubricate the aft engine bearing.  This oil was discharged into the jet exhaust, and never seen or heard from again.  To this day, this is still true.  You must service the engine oil almost each flight.  Other than this, it was really a good engine in it's day.
    The Viper Engine has a "Top Temp Limiting" device that limits fuel flow such that you do not exceed the maximum engine exhaust gas temperature during takeoff, or during climb, as you select on the three position switch that controls the system.  You have "Takeoff", "Climb", and "Off" positions.
    On the old Hawkers, you must make sure that the correct engine start mode is selected, or the engines will not crank.  GPU starts are made with the switch in "Norm", and battery starts are made with the switch in "Internal".  If one of these two does not work, check the voltage on your 3rd battery!  It is used to power the start relay.  No # 3 Batery, no engine start!
    Some of the 1a airplanes have been fitted with the TFE-731 engine.  This makes for a stage 3 airplane as far as noise goes, and extends the range quite a bit.  A 1a fan will burn about 1800 lbs the first hour and 1400 lbs thereafter.  It will go about 4.5 hours at a little over 400 knots.
 

Center Panel

 
Fuel System

 The HS-125 carries it’s fuel in the wings, and on most of the newer models, in a verteral tank.  The 1A model has wing tanks only.  The fuel is supplied to the engine driven fuel pumps by an electric boost pump located in each wing tank.  Two valves are installed between the respective sides of the fuel system.  The "Crossfeed " valve allows feeding of one engine from the opposite tank, and feeding both engines from a single tank.  The "Interconnect" valve allows transfer from one tank to another.
 To "Crossfeed", place the fuel Crossfeed / Transfer lever to the first detent.  This opens the crossfeed valve.  Leave the boost pump ON in the tank you wish to feed from.  Turn the opposite boost pump off.  The operating boost pump provides fuel to any engines that are running.
 To "Transfer" fuel, place the fuel Crossfeed / Transfer lever to the "Interconnect" position.  This opens both the crossfeed and transfer valves.  Leave the boost pump on in the tank you wish to transfer TO!  Turn off the pump on the side from which you wish to extract the fuel.  Remember, always open the valves prior to turning off any pumps, and turn on all pumps before closing any valves.
 

Fuel Filter De-Ice / Viper Powered Only

 Methyl alcohol is provided to de-ice the fuel filters.  This alcohol is pumped from a reservoir located on the side of the fuselage at the trailing edge of the right wing under the engine nacelle.  Use fuel filter de-ice any time you get a fuel filter clogging light.  Just prior to descent, use 3 seconds of fuel filter de-ice, then switch to "Auto" for the remainder of the descent.  Some like to just set the switch to "Auto" for the duration of the flight.  I prefer not to do this, as you may run out of fluid and not know it until it’s too late.  My recommendation is to leave it off during climb and cruise, give it about a 5 second blast at top of descent, then "Auto" for the descent.  This way a malfunction should not rob you of your engines due to ice clogging the fuel filter.  These recommendations are as a result of experience with the airplane.
 
Electrical System

 

Hawker 1a Overhead Panel
 

The HS-125 is equipped with two starter generators, two main batteries, and a third battery.  The main batteries provide emergency power in the event both generators are lost, and give you internal start capability.  The third battery has the sole duty of operating the start relays.  This prevents the start relay from opening and closing during engine cranking due to a drop in battery voltage.  If the third battery is dead, the engines won’t start, even with a GPU, as the start relay will not close.   The loss of one generator will not cause loss of any equipment, as the "Bus Tie" relay will close, indicated by illumination of the amber Bus Tie light.

Viper Powered Aircraft
Ground Operation 110 Amps 5 Min
80 Amps Cont
Flight 235 Amps Max

 

Hydraulic System

Main
 The main hydraulic system on the HS-125 uses 5606 fluid.  It operates the landing gear, brakes, flaps, airbrakes, lift dump, and nosewheel steering systems. There is an emergency system that may be used to lower the landing gear, and operate the wing flap system.

 The main system has an engine driven pump on each engine, and a hydraulic reservoir in the tailcone.  There are cockpit indicators that tell you if each hydraulic pump is operating.  They are mechanical, and will read "NORM" or "FAIL" depending upon the output flow of the respective hydraulic pump.  The main system is used to charge the brake accumulator to provide a parking brake, and emergency braking if the main hydraulic system fails, or is just not operating, such as on the ground prior to engine start.  This system may be charged by a hand pump located in the tail of the airplane.  This is not to be confused with the "Emergency " system.  The hand pump in the tail provides pressure to the main system, but at a lower rate than the engine driven pumps, unless you are Charles Atlas on steroids!  The hand pump in the cockpit operates the emergency system only.

Emergency
 The emergency hydraulic system will lower the landing gear, and operate the wing flaps.  To activate the system, place the gear switch down, pull the emergency gear extension handle on the left side of the throttle quadrant, and pump.  The gear will come down slowly, as you operate the hand pump.  To operate the flaps, merely select the flap position you desire, and operate the hand pump until the flaps reach that position.  The flaps may be raised or lowered, however the landing gear may only be extended with the emergency system.  The emergency system reservoir is in the nosewheel well.  It is depleted when the emergency system is used, so if you pump the flaps to check the system, have maintenance check and possibly service the emergency reservoir.
 
 

Flight Controls

 The ailerons and elevator and rudder on the HS-125 are manually actuated by the pilots.  The aircraft does have an autopilot.  The ailerons and elevator may be moved by the autopilot servos, and the rudder is equipped with a yaw damper, and a rudder bias system.

Rudder Bias


 The rudder bias system uses engine bleed air to reduce the required rudder force during flight with one engine failed, or producing substantially less thrust than another.  Bleed air from the right engine applies right rudder, and bleed air from the left engine applies left rudder.  When both engines are operating, the net result is zero.  When one engine fails, the bleed air from the operating engine applies a force moving the rudder toward the operating engine.  The Jetstar and King Air have similar systems.  These type systems are about as reliable as an iron ball.  Not much to go wrong here!

Flaps


 The flap system is hydraulic.  The flaps may be extended or retracted by the main or emergency hydraulic systems.   The flaps are also a component of the "Lift Dump" system.  Do not extend flaps when airbrake is extended.

Airbrake


 The airbrake system consists of panels located on the upper surface of each wing.  They are hydraulically actuated by a single "Airbrake / Lift Dump" handle in the cockpit.  The airbrake must be in the retracted position whenever flaps are extended.  The only exception to this is during the landing roll.

Lift Dump


 The Lift Dump system consists of the flaps, and the airbrake.  Lift Dump may be selected only when the flaps are in the fully extended position.  After landing, apply the airbrake.  When it reaches the aft stop, pull the lever slightly up, and then aft and down.  This extends the flaps to a nearly vertical position, and substantially increases drag.  You will be surprised at how effective they are.  Do not attempt to retract the flaps until the airbrake handle has been placed to the stowed position.

Nosewheel Steering


 The nosewheel steering system is hydraulic, and works with pressure from the main system.  If the main system pressure is lost, the nosewheel steering will be inop.
To cope with this, you have two options once you have lost rudder effectiveness, let the airplane go where it wants, or use differential braking.  The second option is the wiser one.   The emergency  braking system will allow this.

Brakes


 The normal braking system provides braking to all of the main gear wheels.   Anti skid protection is provided by mechanical devices located in the axles.  Emergency brakes and parking brake is provided by an accumulator that is charged by the main system.  With the brake control lever full forward, the normal brakes function as dictated by the pressure on the brake pedals.  With the brake control lever in the center, or first detent, the emergency brakes work, again, as dictated by the brake pedals.  Anti-Skid is not available when emergency brakes are in use.  Pull the lever full aft, and the parking brake is engaged.  If this is done with the aircraft in motion, the tires won’t like you much.  Neither will the passengers for that matter.  If the brake accumulator is discharged, pump the pressure up with the handle in the tailcone.  This may prevent some excitement when the engines are started.
 
Performance

At 21,200 lbs Flaps 15
Sea Level  15 Deg C 4,700 ft  Runway Required
                 20 Deg C 5,200 ft Runway Required
Above 20 Deg C
 Climb Limited @ 15 deg Flap
 Accelerate Stop distance is not limiting at any legal takeoff weight for a flaps 15 Deg takeoff.

 Stall Speeds
Vs @ 15,000 lbs  
Flap   0 Deg
91 kts
Flap  15 Deg 
85 kts
Flap  25 Deg
83 kts
Flap  50 Deg
82 kts

 These stall speeds increase 3 kts per 1,000 lbs above 15,000 lbs.  So at 20,000 lbs, the 1 G flaps up stall speed is (5 x 3)+(91) = 106 kts.  This is accurate to within about one knot.