Have you ever been standing near a heliport or a hospital and looked at the helicopter as it took off and wondered why is it taking off in reverse? I thought the same until I moved into a MedEvac helicopter and it all became clear. There is a method to the apparent madness I assure you!
Helicopters take off backward to allow the pilot to keep the helipad in sight in case they need to re-land in an emergency. When taking off vertically, the helipad disappears out of sight around 30ft to 50ft up, backing up allows the pilot to keep the helipad in sight through the chin bubble window.
Not sure what I’m talking about, watch this video…
Read on to find out exactly why helicopters sometimes back up and sometimes they don’t…
Why Do Some Helicopters Reverse When Taking Off?
There are two main reasons why a helicopter will lift off and reverse before flying away:
- The path in front of them is blocked by obstacles which they need to navigate around, or
- The helipad is the only clear spot the pilot can return to in the event of an emergency happening during takeoff
1. Obstacles In Front
This image above shows the route in front of the helicopter is blocked by the very tall buildings in Manhattan, so the only way for the pilot to take off is to reverse out over the Hudson River, turn and then depart.
For the pilot to climb vertically and then fly over the top of the buildings in front of them is not a safe departure. Helicopters use the most amount of power when they are hovering or climbing vertically with no airspeed.
The safest option is to reverse out, turn, and then accelerate while climbing along the river before turning over the buildings once the helicopter has climbed to a safe altitude. This would also be quicker, especially if the helicopter is heavy on fuel and passengers as a vertical climb would be slow.
Vertical climbs work fine when the obstacle/s is only several hundred feet high, like a MedEvac helicopter departing a scene call surrounded by trees or lower buildings or when the helicopter is coming out of a confined area and there is no room to back up.
2. Return To Helipad
This scenario is the most common reason why you will see a helicopter reversing while departing and it is to allow the pilot to go back to the helipad in the event of an emergency occurring during takeoff.
When the helipad is the only available spot to land in the event of an emergency occurring, the pilot has to maneuver the helicopter to be in a position to make it back to that same spot they just departed from if anything were to happen.
Helipads on top of buildings, helipads on offshore platforms or even landing spots in built-up areas are all examples of landing locations with no other alternatives.
Reversing Vs Climbing Vertically
Taking off in a helicopter means clearing all obstacles on the departure path with room to spare or returning back to the pad – Simple. The only way to ensure any obstacles are cleared is to climb high enough before flying away, but this presents a problem with tall obstacles.
As the pilot climbs the helicopter vertically, the helipad will begin to disappear out of sight below them at around 30-50ft (helicopter dependant) because their field of view is restricted to what they can see by looking forward, sideways, or down through the chin bubble window (The window by their feet):
Not being able to see the helipad makes it difficult for the pilot to return to it in the seconds following an engine failure. There is alot to do when an engine quits with only seconds to complete it in, having to now find the helipad below them really increases the chances of an unsuccessful landing.
To overcome this, a ‘Back-Up’ style departure is used:
By reversing the helicopter, it keeps the helipad in sight via the chin bubble window. This allows the pilot to climb to any altitude to be able to clear the obstacle all while keeping the helipad in sight.
There are manufacturer recommended takeoff profiles that pilots should follow to allow their helicopter to accomplish both vertical and back-up departures:
Single Engine Helicopters
Flying away from an engine failure when you only have one engine is just not going to happen! The only option the pilot has is to descend back to the spot they took off from.
Once a helicopter with one engine climbs vertically above 20ft, making a successful engine off landing without damaging the aircraft start to dramatically decline.
By reversing in a single-engine helicopter, it allows the pilot the opportunity to drop the nose of the helicopter and gain a little bit of airspeed as they autorotate towards the pad. This little bit of airspeed can really help cushion the landing if the engine were to quit during the departure, even then, the chances of no damage are slim.
For this reason, twin-engine helicopters are a better choice for operating in built-up areas.
Twin Engine Helicopters
Having a second engine really increases the safety factor hence why most helicopters that operate, land and takeoff in congested and built-up areas are mostly twins.
Each helicopter manufacturer publishes recommended takeoff and landing profiles for their helicopters to give the pilots the option of safely returning back to the helipad or flying away depending on when an engine failure occurs. The heights the helicopter climbs to can vary depending on the helicopter type.
Flying away can only be completed providing any obstacle in front of the helicopter can be cleared. The height of that obstacle in the departure path will dictate if the helicopter climbs vertically and departs or whether it reverses and then departs.
This is a typical Vertical Takeoff profile where the helicopter climbs straight up to a maximum of 70ft (Leonardo Helicopters) before flying away. If an engine quits before reaching the top of the vertical climb (TDP), the pilot descends back to the pad using the second engine.
If the engine quits after reaching TDP (Takeoff Decision Point) then the pilot drops the nose, accelerates, and flies away on the remaining engine. The obstacle height and distance from the pad will be calulated by the pilot before taking off.
When Do Helicopters Need To Take Off In Reverse?
The decision to do a reverse takeoff will be dictated by the takeoff profile requirements issued by the manufacturer and it all has to do with what obstacle/s, if any are in the departure path of the helicopter.
If the helicoter is departing off a rooftop helipad with no obstacles that are higher than the pad, then a small vertical climb to 30-50ft before accelerating away will be most commonly used.
However, if the helipad is surrounded by taller buildings, trees or towers then the pilot will need to do a back-up or reverse takeoff profile.
Let’s look at the Backup Takeoff Profile for the Leonardo AW139 – If the obstacle requires the helicopter to climb more than 70ft vertically above the helipad, then the Back-Up Takeoff profile will be used – Again so the pilot can keep the helipad in view while they reverse.
Before takeoff, the pilot looks at the obstacle in front of them and roughly calculates its height above the takeoff point. The helicopter will be required to climb to approximately 50ft higher then the calculated height of the obstacle before accelerating into forwarding flight:
- Obstacle within Take-Off Distance = 65ft higher than the Helipad
- Obstacle Height + 15ft drop for pilot reaction time if an engine fails
- Obstacle Height + additional 35ft for helicopter descent while accelerating on one engine – (20ft for acceleration drop & 15ft obstacle clearance)
∴ The pilot needs to add 50ft to the obstacle height – this will give them the height needed to climb to before reaching the TDP and accelerating away.
TDP for this example would be 65ft(obstacle height)+50ft(profile recommendation height) = 115ft TDP to clear the obstacle by 15ft if the engine were to quit right at TDP.
The engine fails before TDP the pilot returns back to the helipad using the second engine.
This is known as a Category A Takeoff Profile and if flown as depicted in the manufacturer’s recommended profile it will ensure the helicopter will clear the obstacle by 15ft. CAT A takeoff and landing profiles are used extensively in Twin-Engine helicopters.
Can Helicopters Fly Backward?
Helicopters can fly in any direction, especially backwards. The main rotor system does not know which is forwards or backwards. Flying backwards means no visibility for the pilot and requires more control on the pedals as the helicopter will want to weathercock into the direction of travel.
The only thing that dictates which way the helicopter is going is the direction the pilot is looking. Flying sideward, forward or backward makes no difference to the main rotor system as it is tilted in the direction the pilot wishes to move.
While maneuvering a helicopter in a hover many pilots will reverse their helicopter to place it over the required spot once they have completed a turn to ensure the area behind is all clear. Not being able to see is by far the biggest factor in flying a helicopter backwards.
The most common type of backward flying you may see after helicopters taking off is when they are utilized to string cables between towers. The helicopter will ‘Pull’ the cable from a spool and place it over the supporting arms of the tower. This will be repeated down the line of towers until the cable is in place.
To prevent a collision of the cable with the tail rotor the pilot will fly the helicopter backward. This is a slow and controlled flight and takes great skill and patience.
Here is a great video of an AS350 Astar pulling a cable with the pilot talking about what he is doing:
If a pilot wishes to fly the helicopter in reverse and at high speed the rear vertical stabilizer will want to try and turn the nose into the direction of travel. They are designed to help keep pointing the fuselage straight ahead and by flowing air across it in the opposite direction it will try and weathercock.
To prevent this the pilot will have to use very controlled, but forceful pedal inputs. This puts stress on the tail rotor system and to be honest there are not really any reasons why a pilot would need to fly fast in reverse, especially for a long period of time!
Try These Articles:
* This is why a helicopter MUST have 2 propellers or does it??
* How Do Helicopters Use Hydraulics?