CHAPI Heliport Approach Path Indicators ZA757 and ZA737

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Read the Right Glide Slope From Over Ten Miles Out!

The heliport approach path indicator (CHAPI) provides the pilot with a safe and accurate glide slope on final approach to the helipad. A row of CHAPI light housing assemblies (LHAs) placed perpendicular to the approach path are seen by the pilot in combinations of red, green, and white to indicate a path that is too high, too low or correctly on slope.

The CHAPI system has a filter inserted between the white and red filters of each lens to provide a 2° wide green sector that, when visible from both units, signals the proper glide slope angle of 6°. Angle deviations that are too high show one or two white lights, and those that are too low show one or two red lights.

Configuration Options

The CHAPI uses only two LHAs and provides simplified glide slope information. The CHAPI can be configured to read white/green/red for use on heliports. The LHAs use either 2 lamps (ZA757) or 3 lamps (ZA737). The 3 lamp configuration permits normal operation with one lamp out.

Power Options

Three energy styles are available:
Style A operates from a 240VAC (120V is also available), single phase, 60 Hz power supply. 120V and 50Hz are also available.

Style B is current powered and operates on 6.6 amp series circuits from an L828 constant current regulator. Lamp brightness is controlled by the output setting on the regulator.

Style C is a 48V system powered by auto batteries. This style is of particular value on remote airstrips where it would be uneconomical to bring in power lines.

Operating Conditions

CHAPIs are manufactured to meet two temperature standards: Class I for normal operation to as low as -35° C, and Class II, with lens heaters, for temperatures to -55° C.


Flight Light/ALSTOM CHAPIs have the most reliable photometrics in the industry. On a normal day a 2-lamp CHAPI unit is visible from over 10 miles out. Light distribution curves far exceed FAA requirements.

For FAA style units, a tilt-switch in each CHAPI shuts down the entire system if any unit becomes misaligned.


Performance Advantages

• Outstanding photometric performance. Pilots say they see this CHAPI before they see any competing brand.
• Four-leg design makes each light housing assembly very stable, resulting in fewer shut-downs for realignment thereby reducing maintenance and increasing airfield utilization. (EMT legs not included with domestic orders.)
• LED indicator identifies tilt switch circuit fault.
• Quartz halogen average rated lamp life is 1200 hours! Competitor's lamps rated at only 1000 hours.

Maintenance Advantages

• Dust proof LHA is standard. Enhances lamp life, improves photometric performance and reduces maintenance cost.
• No optical bench or special tools required for servicing. Special access doors speed lamp changes in the field.
• Off-the-shelf lamps reduce life-cycle costs.
• Circuit breaker and on/off switch in power adapter (Style A) and in each LHA (Style B) protect equipment at all times.
• Extremely reliable power adapter features WAGO terminal blocks, gas-tight ferrelled connections and Teflon wire.


• Custom configured remote control uses radio modems instead of hard wiring to control CHAPIs.
• Aiming device kit (with spirit level) simplifies setting tilt switch and azimuth angles. Lamps are adjusted to the correct glide slope angle (± 3' of arc).
• ICAO version (no tilt switch)
• International packing - four 2" EMT legs per LHA with all units and hardware double boxed.

CHAPI: Cramp's Helipad Approach Path Indicator

The 'C' in CHAPI stands for 'Cramp', the name of person who invented the system 40 years ago to help train pilots returning from Vietnam. Dave Cramp was a training captain for Bristow Helicopters in Dubai, "I was tasked with training ex-Vietnam pilots we had just employed. They were all very experienced pilots, but they had problems flying in a civilian environment where they weren't being fired at. My job was to 'civilianize' them. The big problem was getting them to fly steep approaches instead of coming in very low with a big flare just before 'crashing' on to the helipad. I needed a way to get them to see and adopt a 6 degree slope. Hence the CHAPI. It was originally made of wood with a slot at the front. My next prototype was constructed out of a plastic water container. I used this for 3 years before a company in Rugby, UK offered to further develop the device. The first commercial sale was to Aberdeen Airport in Scotland in 1982 and it is still being used there today."

CHAPI Wiring Connections

Tilt Switch Circuit

Powering LHA 1

Powering LHA 2

Interruptor de inclinacion (Español)

Alimentacion de la caja LHA 1 (Español)

Alimentacion de la caja LHA 2 (Español)

CHAPI Troubleshooting

Tilt Switch Circuit

LHA Alignment

Standard Features

• Fully gasketed dust proof light housing assembly (LHA) improves performance and reduces maintenance (standard feature).
• Large lens overhang and optional heaters forward of the lenses allow continuous operation under severe arctic conditions.
• Input power: 2-Box CHAPI 1,000 VA
• Standard input voltage: 240 VAC, ±10%
• Lamps: 200 watts, 6.6 amp quartz halogen
• Rated lamp life: 1,200 hours
• Environmental operating conditions:
- Class I: +55° to -35° C (+131° to -31° F)
- Class II: +55° to -55° C (+131° to -67° F)
- Humidity: 0% to 100%
- Wind: 100 mph (161 km/hr)
• Easy to maintain and relamp

Common Renewal Parts

Part Number Part Description
LA-6373 Lamps: 200 W 6.6A quartz
15-FFF2X425 Frangible cast aluminum floor flange
15-201TSA Tilt switch assembly
77-104FAANTD Photo control 208-277 VAC
80-019035 Filter glass, red - ZA757/4
80-021253 Filter spring - ZA757/4
80-021254 Reflector assembly - ZA757/4
77-RH25.47 Resistor - 25 W, 0.47 ohm (lens heater Class 2 only)
77-W199AX-15 Relay, contactor - 30 amp DPDT, 240 VAC
77-777-310 Tool for WAGO terminal blocks
77-RTE-P21 Timer, D-O-B adjustable - 24 VAC/DC
77-TB20199 Photo control base
77-#98-6 Precision spirit level, 6"

Packing Specifications

Description ZA757 ZA737
Number of lamps 2 3
Net weight in lb. 42 55
Gross weight in lb. 53 75
Length in inches 48 48
Width in inches 22 32
Height in inches 15 15
Volume in cubic yd. 0.34 0.50
Lamp 2x200W/6.6A 3x200W/6.6A
Type LA-6373 LA-6373
Transformer 2x200W/6.6A 3x200W/6.6A

CHAPI (Style A) Troubleshooting

Very few problems will occur with your system. However, in the case of problems, the following pointers will help you locate and correct the problems. It is assumed that all interconnect wiring is good and that tilt switches are aligned and have continuity.

Symptom Likely Problem
Lamp 'OUT' Check lamp (if either lamp burns out, it would not shut off the other lamp).

PEC operation reversed
(dim in daylight)
Check wiring of PEC to TB3 (color coded red/blk/wht).

Lamp still not 'ON' Temporarily short TB1B, R1-1 and R1-2, then R2-1 and R2-2. As each is tested, if the failed lamp turns 'ON', the heater resistor may have failed. Check for .5 ohm resistance - replace if required.

Lamps do not burn
(RTE-P21 mode light out)
Temporarily short Power Supply TB1 T-1 and TB1 T-2 and engage CB1. If system now functions, problem is either switches or tilt switch wiring. If problem is determined to be a particular tilt switch, readjust tilt switch by going through zero and then back. DO NOT LEAVE JUMPER IN PLACE!

Light Box Alignment Footers not stable. Mounting hardware is not tight. Check floor flanges, nuts on frangible couplings, bolts & nuts on light box.


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