SUBJECT - COMPLIANCE WITH INSTRUMENT FLIGHT RULES
INTRODUCTION - REGIONAL AIRLINES SAFETY STUDY
Between October 1995 and July 1997 the Bureau of Air Safety
Investigation undertook a study of the safety of Australian
regional airlines. The objectives of this study were to:
(a) identify safety deficiencies affecting regional airline
operations in Australia; and
(b) identify means of reducing the impact on safety of these
For the purposes of the survey, regional airlines were grouped
according to the number of passenger seats fitted to the largest
aircraft operated by that airline in January 1997. The groups are
defined as follows:
(a) group 1: 1-9 seats;
(b) group 2: 10-19 seats; and
(c) group 3: more than 20 seats.
The study involved analysing data obtained from:
(a) responses to a survey of Australian regional airline
(b) discussions with Australian regional airline employees and
(c) air safety occurrence reports involving regional airlines over
a 10-year period (1986-1995) from the BASI database.
This Safety Advisory Notice addresses one of the safety
deficiencies identified as a result of this study.
Some pilots are intentionally descending below published safety
altitudes in conditions under which terrain clearance cannot be
When respondents were asked to describe a safety incident,
occurrences of pilots breaking instrument flight rules (IFR)
constituted one of the most common types of incident described.
Pilots were asked to agree or disagree with the statement that
their company flies strictly by the IFR. The large majority of
pilots (94.7%) agreed with this statement, while 4.1% disagreed.
When the responses to this question were analysed by airline group,
there was no significant difference between the answers from pilots
from the three airline groups.
Pilots were also asked to describe any deviations from the IFR,
and the reasons for these deviations. A numerical summary of the
responses can be found in attachment 1.
Descent Below Safety Altitudes
From the survey responses, some of the deviations involving
descent below a published safety altitude included:
(1) descent below the steps during a Distance Measuring Equipment
(DME) or Global Positioning System (GPS) arrival while in
instrument meteorological conditions (IMC);
(2) descent to circuit altitude at night outside the instrument
approach circling area;
(3) descent below instrument approach minimum descent altitude
(MDA) while in IMC; and
(4) diversion off-track to descend in IMC over water to an
altitude lower than the destination MDA.
For the purpose of this study, "safety altitude" is a generic term
meaning "lowest safe altitude", "minimum safe altitude", "minimum
altitude" for a given DME/GPS distance in an arrival procedure or
"minimum descent altitude" in an instrument approach.
Examples of survey responses
"When breaking clear of cloud, [there is a] tendency to adopt
visual procedures with little or no forward visibility in rain. If
not visual upon reaching minimum altitude, a large number of
captains immediately descend further. [This is caused by] lazy,
undisciplined captains and a perceived "uncoolness" in just missing
- Pilot, respondent 085
"[A common deviation from IFR is] descent below the lowest safe
altitude on route sectors to aerodromes without a navigation aid in
conditions that are non-VMC. [This is done] to enable the flight to
get into an aerodrome where conditions are marginal but is not
surrounded by terrain or obstacles."
- Pilot, respondent 178
"One or two management pilots have a willingness to push the
minimums i.e. they suffer from get-in-at-all-costs. Old habits die
hard. One suffers tunnel vision and talks himself into continuing,
for example, "it is only a couple of hundred feet", "you've done it
before", "one must be flexible" and "the rules are only a
- Pilot, respondent 568
Descent below the published safety altitude has been a factor in
many accidents, including the crash of the Monarch Airlines Piper
Chieftain at Young, NSW in June 1993. Any descent below the safety
altitude, in conditions under which terrain clearance cannot be
assured, increases the risk of a
controlled-flight-into-terrain-accident, and represents a
significant safety issue.