During the last decennia,the debate on the respective benefits of Airdrop (A/D) and Airlift (A/L) has increased concurrently with the need of aerial food delivery. Controversy has been going on for a long time, sometimes based on wrong assumptions. In view of its long-term experience in delivering food with transport aircraft, WFP is in a position to make an objective comparison between the two types of aerial food delivery.

a. Airdrop disadvantages.

Cost. A major disadvantage of airdrop is that the food commodities have to be packed in multiple and special bags and that for most of the dropping methods dispensable airdrop pallets are required. This makes airdrop food packing USD 50 per MT more expensive than airlift.
Losses. A certain percentage of food will be lost because of dispersion and/or rupture of the sacks on impact. With current airdrop techniques the average loss is 0.5%.
Flying time.
Some operators perform several dropping runs which result in an augmentation of flying time.

b. Airdrop advantages.

Access to populations. Dropping Zone (DZ) requirements are less restrictive than airfield requirements. Consequently, it is possible to select DZ at places where direct food distribution is possible under permanent control of the WFP staff. One of the major advantages of A/D is that people can stay in their usual environment that normal life patterns are not disrupted.
Secondary transport. Airlift will require secondary transport to further distribute the food. In the case of isolated towns, fuel for trucks may have to be airlifted, entailing additional costs. If secondary transport is not available, the population will concentrate in the areas surrounding the main airports and, consequently, totally depend on relief aid.
Maintenance costs. Airlift to airports with sub-standard runways drastically increases maintenance costs as tires, brakes, engines and undercarriage will suffer from ingestion of dust, projection of stones, etc. Some operators augment their lease rate with 30%.
Flight safety.The risk of accidents is higher for Airlift operations, in particular on sub-standard runways. In addition, because of the greater exposure of aircraft to security risks (hijacking/shooting), the insurance rates for Airlift will be significantly higher than for Airdrop. Ground costs. Airlift operations may be subject to outrageous landing, security and handling fees, such as it was the case during the operations in Somalia in 1992.
Rotation time. When performing Airdrop, the flight time of some operators will be higher than for Airlift, in particular when they make several dropping runs. On the other hand, no time is lost for downloading on the ground. Consequently, the total rotation time for airdrop operations is shorter than for airlift, allowing a more intensive use of the aircraft.

c. All the elements mentioned above should be taken into consideration and the cost-effectiveness should be carefully calculated. In most cases, considering all associated costs of airlift, airdrop will turn out to be the most cost-effective option.

d. It should be kept in mind that it is not possible to switch from airlift to airdrop in a matter of days. The dropping of large quantities of food requires careful preparation which might take up several weeks. Nevertheless, some types of food can be pre-stored and stand-by arrangements with manufacturers can be made. This should reduce the preparation time to an absolute minimum.

3. Types of airdrop.

Different airdrop methods are being practiced. The choice of the method will depend on several factors such as costs, availability of dropping zones and presence of monitors, flight safety, aircraft security, concentration of recipients, etc. The three major categories of dropping methods are the gravity extraction method, the parachute method and the Lightweight Food Delivery (LFD) method. The advantages and disadvantages are briefly discussed below.

a. Gravity extraction.

There are currently 2 methods in use to drop food in relatively large bags, the normal dropping method from an altitude of approximately 800 feet above ground level and the Very Low Altitude Gravity Extraction System (VLAGES) method.

(1) Very good results have been achieved with normal droppings from 800-1000 feet. The food (wheat, rice, etc.) is packed into bags that have a capacity of 70/80 kg, but only filled up to 50 Kg and subsequently inserted into three outside bags. To prevent ‘explosion’ upon impact, the inside bags are cut before insertion into the outside bags. With VLAGES, the aircraft drops the load at an altitude of 50 feet. Because of the low altitude and the short time of fall, the food bags hit the ground at a relatively low vertical velocity but the horizontal speed at impact is high. The conditioning of the food bags is similar to the normal method with the exception that only 25 Kg of food is packed in the inside bag that has a capacity of 50 kg.
(2)The normal dropping method from 800 feet is less expensive in packing material than VLAGES, the loading and recovery of the bags is easier and quicker while the losses upon impact are very similar. The normal dropping method is less accurate than VLAGES, but the technique can be applied if the DZ is well secluded and the security measures sufficient to prevent the intrusion of people during the dropping phase. When deciding to proceed with gravity extraction droppings in large quantities, the normal delivery method should have preference over VLAGES, except if the DZ is very small (i.e. small table top mountain in Ethiopia).

b. Parachute dropping.

The parachute dropping system consists of pallets that are attached to a parachute and contain maximum one ton of tightly strapped cargo. The parachute should be considered as lost after dropping. The dropping method is very inaccurate (the parachutes and pallets drift with the wind) and could be dangerous for people on the ground. Another disadvantage is that there is no control over the food distribution. Dropping with parachutes should only be envisaged as a last resort. Parachuting comes into consideration when urgent delicate material like medicines need to be brought to isolated places, where no other means of delivery exists.

c. Lightweight Food Delivery (LFD).

(1) A third method is the LFD system. It consists of dropping individual rations of dry food, packed in plastic bags. The packets are made in such a way that they will float or spin to the ground at a reduced, safe speed. The package can be made waterproof and will float on the water.
(2) The dropping is done at medium to high altitude and the rations are randomly spread in the crisis area. The method can be used for reaching needy populations for short periods of time when no other options exist i.e.
-  Monitors cannot be fielded in the area of intervention;
-  Security of the area is endangered by anti aircraft devices;
-  Creation of an appropriate and secure drop site is impossible due to terrain conditions;
-  Use of conventional airdrop technique would represent a risk for the beneficiaries of the dropping zone due to lack of infrastructure, natural  disaster, insecurity, inaccessibility, etc.
(3) Another advantage of the system is the fact that food is scattered over a broad area, reducing the risk that a small group among the population could control the food distribution and augmenting the probability of obtaining a fair distribution among the population.
 
4. Selection of the airdrop method.

Multiple elements will have to be considered when recommending the most appropriate airdrop method. This quick reference should help to make the selection, but other elements should be taken into account; such as:
-  Availability of certified aircraft and qualified aircrew;
-  Availability of technical support equipment;
-  Availability of qualified technical support personnel;
 - Availability of food packages, which may be a major issue in LFD.

Normal Food Dropping Requirements and Procedures.

1. General.

a. Normal in-flight food dropping implies a geographically suitable DZ, an obstacle free approach and sufficient airspace to manoeuvre the aircraft into the dropping position. In addition, the area behind the DZ should be kept clear because a late drop due to human error or technical failure could have disastrous consequences. The DZ should be away from buildings, village centres or any area where it is difficult to police the zone.

b.The requirements for obstacle and free approach will augment inversely proportional to the dropping altitude i.e. the lower the dropping altitude, the fewer obstacles should be in the approach and the more airspace will be required. For Very Low Altitude Extraction System (VLAGES), the ± 1.1 NM (2 km) long approach sector should be free of obstacles. This does not mean that it must be completely flat but the aircraft must be able to follow a path from about 500 feet above ground down to 50 ft at the DZ, with sufficient terrain clearance. This is one of the main disadvantages of VLAGES.

c. Dropping zones should be selected, either in function of the prevailing wind or, if the wind is not a prevailing factor, have a North/South orientation. The latter will prevent that the pilots have to drop into the sun in the morning or late afternoon. On the other hand, if the aircraft can drop in headwind conditions, the horizontal impact speed of the parcels will reduce proportionally and thus causing less damage.

2. Criteria and dimensions.

a. The DZ itself is a rather small zone within a larger safety zone. The DZ for low altitude drops (VLAGES) can be smaller than for medium altitude drops. The VLAGES, the DZ should be minimum 50 m wide and 300 meters long. For normal drops, the DZ should be minimum 200 m wide and 1000 m long. The safety area is an area of 200 m around the perimeter of the DZ. The ideal surface would be of supple consistency whether earth, grass or sand. Hard surface provokes a hard shock on impact. For Low level drops (VLAGES) very soft surfaces like mud or very soft sand are not recommended because it acts like a brake. Especially rocks cause total havoc.

b. Sometimes it is difficult to distinguish the DZ because it is an earth‑coloured area within an earth coloured area presenting itself to the pilots at the most unfavourable angle particularly during drops at low altitude. Maximum effort must be made to present the DZ to the pilot as easy and “eye-catching" as possible. The eye-catching tools will differ with the dropping altitude.

- For VLAGES, the markings should preferably have a vertical development. This can be done by erecting with 3 poles of 1.50 m. height, a pyramid‑like structure covered with polypropylene inside sack material.

- Another system consists of 2 poles well dug in the ground at a distance corresponding to the width of a sac which are then slid upside down over it after having made 2 holes in the corner for the poles. These markings should be put up at the 4 corners of the DZ and if possible in the middle part of it. A white cross should indicate the centre of the DZ. The dropping direction should be indicated by either:

-> A white arrow, pointing in the direction of the white cross at the beginning of the DZ, or

-> Three line-up markers, one at the beginning of the DZ, the second located 75 m behind the white cross (225/575 m from the beginning of the DZ and the third at the end of the DZ.

-> For normal drops (700-1000 Ft) the marking can be put on the ground and secured by stones or other heavy material.

c. A zone of at least 1500 meters behind the centre of the DZ should be prohibited for people and/or domestic animals.

3. Procedures.

a. The initial part of an approach to drop consists of a downwind leg, i.e. with the wind from the back. Its course is parallel to the dropping area in the opposite direction. On this course, speed is reduced in order to allow the opening of the ramp door and setting the flaps. Altitude is 500 to 1000 feet above ground. On the end of this down wind leg follows a shallow turn of 180^o, shallow because of low speed and pallets with sacs which slip in steep turns. For this turn, a space of at least 2 NM (3.7 km) are required. With strong cross winds, an even larger distance is needed to compensate for the drift.

b. During the last part of the final turn the plane establishes its dropping altitude and starts the final approach. For allowing proper line-up during the final approach, the crew must identify the DZ during the base leg turn.

c. Once in final the pilot should acknowledge that he has the DZ in sight and confirm the dropping heading.

4. Communication requirements.

a. Once the decision for air dropping has been taken, it is necessary to contact local authorities in order to obtain permission to operate a mobile aeronautical ground station with its usual VHF frequencies ranging from 117 to 144 MHz. In most cases, it is the Ministry of Foreign Affairs, Ministry of Defence or State Security and certainly the Post & Telecommunication and Civil Aviation Authority who issue these permits.

b. The UN should have its own supply of such VHF air-band transceivers. They should be battery operated and independent from any power supply but need to be recharged overnight from a 220 V source. A small generator is quite sufficient for this task. If equipped with a small whip antenna, additional installations are unnecessary to give the necessary range of 30 to 50 km depending on the terrain. It must be borne in mind that VHF works on a "line of sight" basis and can therefore become very limited as soon as there is an obstacle, like a mountain, in between.

c. Ascertain that the elected frequency with is not in use in the country to avoid unwanted interference which might lead to serious consequences and finally to withdrawal of permission. The person operating this aeronautical VHF radio must not only be in possession of a general Radio Operators licence but, according to the Office Federal de l' Air, be the holder of an aeronautical radio operators licence. Do not attempt under any circumstances to contact the tower or aircraft in flight working directly on any tower frequency.

d. Preferably,the ground controller should also have a portable HF system, not only as back-up for the VHF, but also to be able to talk to the home station and be kept informed of any changes in the schedule.

5. Radio procedures.

a. Initial contact.

- The DZ monitor should announce his position in relation to the DZ.
 
- The DZ monitor will inform on the local weather conditions, including the wind direction and the estimated velocity.

- The Pilot in Command (PIC) will announce the type of drop (1 or 2 runs) and give details on the type of cargo.

b. Mandatory calls.

- PIC calls 10 minutes prior to drop.

- PIC calls 3 minutes prior to drop.

- PIC calls 1 minute prior to drop.

- DZ controller gives clearance to drop.

c. Terminology.

- “Dry run” – The PIC reports that there will be no dropping during the overflight of the DZ.

- “Live run” – the PIC announces that it is his intention to drop his cargo during the next run. This should be announced when calling 3 minutes prior to drop.

- “Clear to drop” Confirmation by the DZ controller that the aircraft is clear to drop. This clearance should be given when the PIC calls at 3 minutes prior to drop and confirmed at the 1-minute call.

- “Negative drop” or “Not clear to drop” The DZ controller does not give the clearance to drop.

- “Safety, safety, safety”- Announcement by the DZ controller that, after the initial clearance to drop, the zone is unclear for any reason. The pilot should acknowledge this call by the transmission “aborting the drop”.

- “Stand by for clearance”- Announcement by the DZ controller to hold until the clearance is given. This call should be acknowledged by the PIC by the transmission “Stand by for clearance”.

- “Committed” PIC informs that the drop cannot be recalled.

- “Confirm”- Asking for confirmation of last given message.

6. Safety.

a. Notify the local population of the expected number of drops during the day. A special warning should be given if one or more drops are expected to deviate from the standard procedures.

b. Bear in mind the attitude of the local population, especially in Africa. All possible precautions around the DZ should be taken. This can be done by putting guards around the DZ.

c. Make sure that security is in place at least one hour before the scheduled drop. Everybody should evacuate outside the safety zone. The drop should be cancelled if no security personnel were available. It should be remembered that a pallet is a flying guillotine with excellent sailing characteristics.

d. Ensure that the aircraft makes a proper dry run i.e. an approach that duplicates as close as possible the actual drop. If the dry run is unsatisfactory, a second dry run should be made.

e. The ground controller should only give his "Clear to drop" when all conditions are met, i.e. the aircraft is properly lined-up and the dropping zone is clear.

f. Collecting the bags should be done after the aircraft has set course back to base. Insist that the Pilot confirms that the drop is completed. The "DZ" must be cleared of merchandise before initiating the next drop.

g. If there should be an accident on the ground after the drop, the DZ controller will inform the PIC and ask him to relay the information to the base. If expecting that a medical evacuation will be necessary, give the coordinates of the nearest airstrip to the PIC.

Material Required For Gravity Extraction Airdrop.

1. Pallets (Skids).

a. Size.

Two types of Pallets, or "Skids" as they are called, are in use depending on whether single or double row operation is used.

- Double row operation requires smaller sizes. Pallets since they are side by side inside the aircraft, 2 times 8 behind each other. They take 1 MT load.

- In the case of single row dropping, the 8 Pallets behind each other which are known as C 8 skids. Their dimension are somewhat larger with 165x120x2 cm, weighing 22.5 kg and take 2 MT.

b. Quality.

The quality of the pallets is important for preventing that the pallets bend and consequently block during the extraction phase. Plywood is the best material since it is relatively hard and therefore less subject to deformation, especially during humid and rainy season. Pallets may be considered as a total write‑off for the operator since over 50 % are usually destroyed and biggest part of those remaining are either partially damaged or deformed. They are, however, very welcome by the beneficiaries either for construction purposes or at least for firewood which is usually in great demand.

2. Bags.

a. Inside bags.

The size of the inside bags employed should have a capacity that is larger than the required volume of food. For VLAGES, the food quantity is approximately 25 Kg, the capacity of the bags should be 50 Kg. Normal droppings are done with 50 Kg of food and require a bag capacity of 90 Kg.

b. Outside bags.

For VLAGES, the outside bags must be of woven Polypropylene with strong lateral seams, weighing 305 gr/m2. For the normal deliveries, the outside bags can be of the same material as the inside bags. Alternatively, jute bags can be used if no other material is available. Losses may be slightly higher and will be fluctuating due the variety of material.

3. Nylon ropes.

Nylon ropes are being used for tying the bags safely to the pallets. Their size is roughly about 2 to 3 mm with a tensile strength of several hundred kg. Since polypropylene is a slippery material it tends to slide off the pallets. Therefore it is better to use nets rather than nylon bands.

4. Nylon bands.

Nylon bands of about 5 cm width, sustaining a enormous static load, serve during dropping as "Gates" as well as static lines. The "Gate" functions as a belt, fixed from one side of the aircraft to the other and tightened behind the last pallet to stop it from rolling back during acceleration, climb out and, most important of all, during the final approach at the DZ after the aircraft assumes a nose-up configuration. This is the only means of preventing the load from leaving the aircraft prematurely. When used as static line it performs exactly the same function as during parachute jumping. It connects the falling body with the aircraft. In our case it is not opening a parachute but cuts the nylon lines which held the bags together on the pallets once they have left the plane and the static line reached the end of its travel.

5. Swivel with cutting device.

A normal swivel like it is used on boats except with the lower portion inner side sharpened in order to act as a knife. One such device is hooked under the crossing point of all static lines, each pallet having its own and connected to a steel cable running inside along the cabin, via the static line.

6. Rubber bands.

Inconspicuous as it is, it is important to hold the snake-like folded static line together on top of the pallet after the swivel is hooked into place. Otherwise the static line may get tangled up during extraction roll, cutting the lines of the pallet unintentionally causing the sacs to slip off. Again a most dangerous situation may occur by obstructing the rolling pallets.

7. Fork lift.

Almost any Fork Lift capable of lifting at least 2 MT will do the job. A section of roller rail must be pushed over the two forks enabling the pallets to roll on and off during loading. They may be withdrawn at convenience. Another valuable asset is the capability to move the forks laterally. This will avoid repeated back ups to archive precise placing of pallets on to the rail in the aircraft.

8. Electric hand drill.

In order to fix the sacs on the pallets with the nylon ropes, as much as 28 holes around the edges of the pallet are required. Having received our pallets from the Belgian RAVAIR detachment, this was already taken care off. In any case, it will be wise to have one on hand as back up.

9. Electric hand sewing machines.

It is a portable unit, 5 kg in weight and available for 220 or 110 V. These machines are very delicate and need continuous attention. To condition between 5000 sacs daily, a minimum of 4 is required. In order to avoid last‑minute surprises, make sure the right needles are available for the thread in use or vice versa.

LFD Operators and Delivery Systems.

1. SAFAIR started developing the Snowdrop system in 1992 and conducted some trials on C 130 in 1993. Although the concept proved to be a success, the delivery method using cardboard boxes was inefficient. SAFAIR built a prototype of a new delivery system and gave a demonstration to WFP early in 1998. The Company is now prepared to further develop, test and finalise the new snowdrop aerial delivery system providing WFP shares the costs of this certification programme.

2.EUCOM (United States- European Command) used what they called a TRIAD (Tri-wall Aerial Delivery) delivery system in Bosnia. The HDRs are stored in a cardboard box which is left open at the top (flaps up to provide for more volume) and wrapped in a parachute cord. When the aircraft (C 130, C 141 or C 17) is over the dropping zone, the box is kicked out of the back of the plane and the cord draws taut, rips the box apart and the HDRs drop individually.

3. The Belgian Air Force developed a similar system. The HDRs are packed in large cardboard boxes holding 3,125 sachets and weighing 0.55 metric tons each. The boxes are put on the roller system and “roll out” of the aircraft. The cargo can hold 16 boxes (15,000 HDRs) and all boxes can be delivered during one overflight. The Belgian Air Force is prepared to make this dropping technique available to other operators.

4. IL 76 Operators may be in a position to apply the dropping technique without important modifications. During a normal food drop with bags of 50 Kg or more, the load is stored on individual pallets of 5 metric tons. During the delivery, the pallets start rolling to the back of the aircraft, hit a barrier and the load is tilted outside while the pallets remain in the aircraft. This delivery system may well be suitable for LFD.

Summarising, the dropping techniques of SAFAIR and IL 76 have the advantage that the cardboard boxes are no longer required. This is an important element when no covered storing facilities are available.