SECURITIES AND EXCHANGE COMMISSION

                              Washington, DC 20549

                  Under the Securities and Exchange Act of 1934

                               (Amendment No. 6 )


                                 WHITTAKER CORP.
                                (Name of Issuer)

                                     Common
                         (Title of Class of Securities)

              Date of Event Which Requires Filing of this Statement
                                December 21, 1998
                 Check the appropriate box to designate the rule
                    pursuant to which this Schedule is filed

                                  Rule13d-2(b)
                                    966680407
                                 (CUSIP NUMBER)














1)       Name of Reporting                       Pioneer
         Person                                  Investment
                                                 Management Inc
         IRS Identification                       (a/k/a Pioneering
         No. of Above                            Management Corp.)
                                                 13-1961193

2)       Check the Appropriate Box               (a)
         of A Member of  Group
         (See Instructions)                      (b)  X

3)       SEC Use Only

4)       Citizenship of Place of
         Organization                            Delaware

         Number of                               (5)  Sole Voting Power  549000
         Shares
         Beneficially Owned                      (6)  Shared Voting      0
                                                 Power
         by Each Reporting
         Person With                             (7)  Sole Dispositive   549000
                                                       Power

                                                 (8)  Shared             0
                                                 Dispositive
                                                        Power

9)       Aggregate Amount Beneficially           549000
         Owned by Each
         Reporting Person

10       Check if the aggregate
         Amount in Row  (9) Exclude Certain
         Shares (See
         Instructions)

11       Percent of Class Represented
         By Amount in Row 9.                     4.84%

12)      Type of Reporting
         Person (See Instructions)               IA









Item 1(a)         Name of Issuer.

                  WHITTAKER CORP.

Item 1(b)         Address of Issuer's Principal Executive Office's

                  Mr.John K. Otto, Chief Financial Officer
                  WHITTAKER CORP.
                  1955 North Surveyors Ave.
                  Simi Valley,  CA   93063

Item 2(a)         Name of Person Filing.
                     Pioneering Investment Management, Inc.  a/k/a
                     Pioneering Management Corp.

Item 2(b)         Address of Principal Business Office:

                  60 State Street, Boston, MA 02109

Item 2(c)         Citizenship:


                    State of Delaware - Pioneer Investment Management ,
                    Inc. a/k/a Pioneering Management Corp


Item 2(d)         Title of Class of Securities.

                  Common Stock

Item 2(e)         CUSIP Number.

                  966680407

Item 3          The person filing this statement pursuant to Rule 13-1(b)
                Or 13d-2 is:

                (d)        Investment  Adviser  registered  under Section 203 of
                           the Investment Advisers Act of 1940.








Item 4.  Ownership

(a)        Amount Beneficially Owned                                     549000

(b)        Percent of Class                                              4.84%


(c)      Number of shares as to which such person has

         (i)      sole power to vote or to direct the vote             549000

         (ii)     shared power to vote or to direct vote               0

         (iii) sole power to dispose or to direct disposition of 549000

         (iv)     shared power to dispose or to direct disposition     0

Item 5.  Ownership of Five Percent or Less of a Class.

If this statement is being filed to report the fact that as of the date
Hereof the reporting person has ceased to be the beneficial owner of more
than five percent of the class of securities, check here:    X



Item 6.  Ownership of More than Five Percent on Behalf of Another Person.

               Inapplicable.

Item 7.  Identification and Classification of the Subsidiary Which Acquired
               the Security Being Reported On By the Parent Holding Company.

               Inapplicable.

Item 8.  Identification and Classification of Members of the Group.

               Inapplicable.

Item 9.  Notice of Dissolution of the Group.

               Inapplicable.






Item 10. Certification.

         By  signing  below I  certify  that,  to the best of my  knowledge  and
belief, the securities referred to above were acquired in the ordinary course of
business  and were not acquired for the purpose of and do not have the effect of
changing or  influencing  the control of the issuer of such  securities and were
not acquired in connection with or as a participant in any  transactions  having
such purposes or effect.

         After reasonable inquiry and to the best of my knowledge and believe, I
certify that the information  set forth in this statement is true,  complete and
correct.


         December 21, 1998
                  Date




         s/Robert P. Nault
         Signature


         Robert P. Nault
         Assistant Secretary
         Type Name and Title