CS-E 790  Ingestion of Rain and Hail

ED Decision 2018/014/R

(a)     All Engines.

(1)     The ingestion of large hailstones (0.8 to 0.9 specific gravity) at the maximum true airspeed, for altitudes up to 4 500 metres, associated with a representative aircraft operating in rough air, with the Engine at Maximum Continuous Power or Thrust, must not cause unacceptable mechanical damage or unacceptable Power or Thrust loss after the ingestion, or require the Engine to be shut down.

         Engine tests must be performed as follows, unless it is agreed that alternative evidence can be used, such as results from other Engine test(s), rig test(s), analysis, or an appropriate combination of these, provided by the applicant from their experience with Engines of comparable size, design, construction, performance and handling characteristics, obtained during development, certification or operation.

         One-half the number of hailstones must be aimed randomly over the inlet face area and the other half aimed at the critical inlet face area. The hailstones must be ingested in a rapid sequence to simulate a hailstone encounter and the number and size of the hailstones must be determined as follows:

(i)      one 25-millimetres diameter hailstone for Engines with inlet throat areas of not more than 0.0645 m²;

(ii)     one 25-millimetres diameter and one 50-millimetres diameter hailstone for each 0.0968 m² of inlet throat area, or fraction thereof, for Engines with inlet throat areas of more than 0.0645 m².

(2)     In addition to complying with CS-E 790(a)(1) and except as provided in CS-E 790(b), it must be shown that each Engine is capable of acceptable operation throughout its specified operating envelope when subjected to sudden encounters with the certification standard concentrations of rain and hail as defined in Appendix A to CS-E. Acceptable Engine operation precludes, during any 3-Minute continuous period in rain and during any 30-Second continuous period in hail, the occurrence of flameout, rundown, continued or non recoverable surge or stall, or loss of acceleration and deceleration capability. It must also be shown after the ingestion that there is no unacceptable mechanical damage, unacceptable power or thrust loss, or other adverse Engine anomalies. (See AMC E 790(a)(2)).

(b)     Engines for Rotorcraft – As an alternative to the specifications specified in CS-E 790(a)(2), but for rotorcraft turbine Engines only, it must be shown that each Engine is capable of acceptable operation during and after the ingestion of rain with an overall ratio of water droplet flow to airflow, by weight, with a uniform distribution at the inlet plane, of at least 4-percent. Acceptable Engine operation precludes flameout, rundown, continued or non-recoverable surge or stall, or loss of acceleration and deceleration capability. It must also be shown after the ingestion that there is no unacceptable mechanical damage, unacceptable power loss, or other adverse Engine anomalies. The rain ingestion must occur under the following static ground-level conditions:

(1)     A normal stabilisation period at Take-off Power without rain ingestion, followed immediately by the suddenly commencing ingestion of rain for three minutes at Take-off Power; then

(2)     Continuation of the rain ingestion during subsequent rapid deceleration to minimum idle power; then

(3)     Continuation of the rain ingestion during three minutes at minimum idle power to be certified for flight operation; then

(4)     Continuation of the rain ingestion during subsequent rapid acceleration to Take-off Power.

(c)      Engines for Supersonic Aeroplanes – In addition to complying with CS-E 790(a)(1) and (a)(2), a separate test for supersonic aeroplane Engines only must be conducted with three hailstones ingested at supersonic cruise velocity, except as provided otherwise in this CS-E 790(c). The Engine operating conditions of rotor speed(s), component loading and component temperatures for this test must be representative of supersonic cruise flight operation. These hailstones must be aimed at the Engine's critical face area and their ingestion must not cause unacceptable mechanical damage or unacceptable thrust loss after the ingestion, or require the Engine to be shut down. The hailstones must be ingested in a rapid sequence to simulate a hailstone encounter and the size of these hailstones must be determined from the linear variation in diameter from 25 millimetres at 10 500 metres to 6 millimetres at 18 000 metres using the diameter corresponding to the lowest expected supersonic cruise altitude. Alternatively, three larger hailstones may be ingested in a rapid sequence at subsonic velocities provided it can be shown that such an ingestion is equivalent to the applicable supersonic ingestion in respect of Engine component loading and strength, the kinetic energy of hailstones and their depth of penetration into the Engine.

(d)     For an Engine that incorporates or requires the use of a protection device, demonstration of the rain and hail ingestion capabilities of the Engine, as required in CS-E 790(a), (b) and (c), may be waived wholly or in part by the Agency if it is shown that –

(1)     The subject rain or hail constituents are of a size that will not pass through the protection device;

(2)     The protection device will withstand the impact of the subject rain or hail constituents; and

(3)     The subject rain or hail constituents stopped by the protection device will not obstruct the flow of induction air into the Engine resulting in damage, power or thrust loss, or other adverse Engine anomalies in excess of what would be accepted in CS-E 790(a), (b) and (c).

[Amdt No: E/1]

[Amdt No: E/5]